research on intermittent fasting shows health benefits

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Research on intermittent fasting shows health benefits

Dietary Restriction Nutrition

Evidence from decades of animal and human research points to wide-ranging health benefits of intermittent fasting, according to an NIA-conducted review of the research, published in the New England Journal of Medicine . Still, more research is needed to determine whether intermittent fasting yields benefits or is even feasible for humans when practiced over the long term, such as for years.

Hundreds of animal studies and scores of human clinical trials have shown that intermittent fasting can lead to improvements in health conditions such as obesity, diabetes, cardiovascular disease, cancers and neurological disorders. The evidence is less clear for lifespan effects. Animal studies have shown mixed results, with sex, food composition, age and genetics among the factors that influence longevity. Human trials have mainly involved relatively short-term interventions and so have not provided evidence of long-term health effects, including effects on lifespan.

The review authors are Rafael de Cabo, Ph.D., of NIA’s Intramural Research Program (IRP) , and Mark P. Mattson, Ph.D., formerly of NIA’s IRP and currently a neuroscientist at the Johns Hopkins University School of Medicine.

Although intermittent fasting often results in reduced calorie consumption, weight loss is not the main driver of the health benefits observed in preclinical and clinical studies, according to the authors. Rather, the key mechanism is metabolic switching, in which fasting triggers the body to switch its source of energy from glucose stored in the liver to ketones, which are stored in fat.

“Ketone bodies are not just fuel used during periods of fasting,” the authors wrote. “They are potent signaling molecules with major effects on cell and organ functions.”

Ketogenesis, or the increase of ketones in the bloodstream, initiates activity in a variety of cellular signaling pathways known to influence health and aging. This activity enhances the body’s defenses against oxidative and metabolic stress and initiates the removal or repair of damaged molecules. The impact of ketogenesis carries over into the non-fasting period and can improve glucose regulation, increase stress resistance and suppress inflammation.

“Repeated exposure to fasting periods results in lasting adaptive responses that confer resistance to subsequent challenges,” the authors explain. The “broad-spectrum benefits” include not only disease resistance but also improved mental and physical performance.

The authors acknowledge impediments to widespread adoption of intermittent fasting: the ingrained practice in developed nations of three meals a day plus snacks (along with the ready availability and marketing of food), the discipline required to shift to a new eating pattern and the lack of physician training on intermittent fasting interventions. The authors suggest that clinicians who prescribe intermittent fasting encourage their patients to adopt a gradual, phased-in schedule in consultation with a dietitian or nutritionist.

In addition to the question of intermittent fasting’s long-term effects in humans, the authors point to two other areas requiring further research. Studies are needed to determine whether this eating pattern is safe for people at a healthy weight, or who are younger or older, since most clinical research so far has been conducted on overweight and middle-aged adults. In addition, research is needed to identify safe, effective medications that mimic the effects of intermittent fasting without the need to substantially change eating habits.

This review article and many of the research studies cited within were supported by NIA.

Reference: De Cabo R and Mattson MP. Effects of intermittent fasting on health, aging, and disease . New England Journal of Medicine . 2019;381(26):2541-2551. doi: 10.1056/NEJMra1905136.

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• Review Article
• Published: 22 February 2022

Clinical application of intermittent fasting for weight loss: progress and future directions

• Krista A. Varady   ORCID: orcid.org/0000-0002-9279-9934 1 ,
• Sofia Cienfuegos 1 ,
• Mark Ezpeleta 1 &
• Kelsey Gabel   ORCID: orcid.org/0000-0003-4613-8892 1  

Nature Reviews Endocrinology volume  18 ,  pages 309–321 ( 2022 ) Cite this article

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Intermittent fasting diets have become very popular in the past few years, as they can produce clinically significant weight loss. These diets can be defined, in the simplest of terms, as periods of fasting alternating with periods of eating. The most studied forms of intermittent fasting include: alternate day fasting (0–500 kcal per ‘fast day’ alternating with ad libitum intake on ‘feast days’); the 5:2 diet (two fast days and five feast days per week) and time-restricted eating (only eating within a prescribed window of time each day). Despite the recent surge in the popularity of fasting, only a few studies have examined the health benefits of these diets in humans. The goal of this Review is to summarize these preliminary findings and give insights into the effects of intermittent fasting on body weight and risk factors for cardiometabolic diseases in humans. This Review also assesses the safety of these regimens, and offers some practical advice for how to incorporate intermittent fasting diets into everyday life. Recommendations for future research are also presented.

The three main forms of intermittent fasting (alternate day fasting, the 5:2 diet and time-restricted eating) produce mild to moderate weight loss (3–8% loss from baseline) over short durations (8–12 weeks).

The degree of weight loss achieved with intermittent fasting is on a par with that achieved with traditional dieting approaches (daily calorie restriction).

The ability of these intermittent fasting protocols to help to manage weight long-term is still poorly understood, as the majority of studies to date have run for short durations.

Some studies demonstrate that intermittent fasting improves cardiometabolic risk factors such as blood pressure, levels of LDL cholesterol and triglycerides, insulin resistance and HbA 1c , while others show no benefit on these parameters.

Intermittent fasting is generally safe and produces few gastrointestinal, neurological, hormonal or metabolic adverse effects.

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Acknowledgements

The authors thank the participants in the trials discussed in this Review for their time and effort. The authors acknowledge support from the National Institute of Diabetes and Digestive and Kidney Diseases (grant no. R01DK119783). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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Varady, K.A., Cienfuegos, S., Ezpeleta, M. et al. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol 18 , 309–321 (2022). https://doi.org/10.1038/s41574-022-00638-x

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DOI : https://doi.org/10.1038/s41574-022-00638-x

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DEAR MAYO CLINIC: Is intermittent fasting for weight loss safe? What are the risks of short-term diets that are very low-calorie?

ANSWER: Recent research has found that using intermittent fasting for weight loss may have some benefits in the short term. But at this point, the long-term effects of this type of diet or other diets that severely restrict calories are not known. To lose weight and keep it off, the best strategy is to adopt healthy eating and exercise habits that you enjoy so you can stick with them over time.

Intermittent fasting currently is a popular trend in dieting. There are several fasting methods people employ for weight loss. Some dieters decrease the amount of time they eat each day to, for example, only six hours in a 24-hour period. Others fast every other day. Another approach is called the 5:2 diet, which involves gradually decreasing daily calories to the point that you're only consuming 500 calories a day for two days each week.

A recently published article assessed a variety of research on intermittent fasting. It found that there are some benefits, at least in the short term, to fasting as opposed to just decreasing calories overall.

It appears that fasting for a short time can produce ketosis — a process that occurs when the body doesn't have enough sugar for energy, so it breaks down stored fat instead, causing an increase in substances called ketones. Fasting also affects metabolic processes in the body. These processes trigger a number of responses, including decreased inflammation, improved blood sugar regulation and better response to physical stress. The research shows intermittent fasting could have other health benefits, as well, but more study is needed.

It is crucial to note, however, that little long-term research has been done on intermittent fasting to examine how it affects people over time. So at this point, it's unclear if there are any long-term health benefits or risks related to this diet technique.

We do know that there are risks involved with certain types of intermittent fasting. For example, a technique called dry fasting that includes restricting fluid intake as well as food intake is dangerous because it can cause severe dehydration and pose serious health concerns. And if you take caloric restriction too far, that can lead to malnutrition.

As you consider weight loss and diets, keep in mind that no one approach works for everyone. But there are some basic principles that you should follow as you decide how to best achieve and maintain a healthy weight. At its core, your diet should support your health overall. There are a variety of diets that can do that, including the Mediterranean diet; the vegetarian diet; the Dietary Approaches to Stop Hypertension, or DASH diet ; and the Mayo Clinic diet . All of these diets have similarities that are greater than their differences. They are based on real food and focus mainly on plant products, such as fruits, vegetables, beans, nuts, whole grains, and healthy fats like olive oil.

In addition, as you incorporate a new diet into your life, it needs to be practical, so that you can sustain it over time. If it is drudgery, or if you feel like you're suffering, it won't work in the long run. Eventually, you're likely to slide back into old habits. If you're considering a new approach to your diet — especially if it's something that could be risky if you don't do it correctly, like intermittent fasting — talk to your health care provider first for guidance on how you can manage it in a healthy way. Keep in mind, too, that choosing to adopt healthy lifestyle choices can and should be an enjoyable way to live. — Dr. Donald Hensrud , General Internal Medicine and Endocrinology, Mayo Clinic, Rochester, Minnesota

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Registered Dietitian’s Guide to Intermittent Fasting

Lifestyle , Nutrition

Intermittent fasting has garnered a lot of attention over the past decade, appearing everywhere from medical research journals to podcasts and talk shows. Reported health benefits include weight loss, reduction in insulin resistance and blood sugar levels, reduction in oxidative stress and inflammation, improvement in several markers for heart disease, enhanced cellular repair, improved brain health, and the potential to extend lifespan. 

Sounds like a golden ticket, right?

Not so fast. Like any other diet plan, intermittent fasting is not one-size-fits-all. Many of the purported benefits of IF are related to its potential influence on hormones, cellular function, and gene expression. However, evidence on these health benefits is limited, and further research is needed on the diet’s overall impact. 

Additionally, the potential risks of intermittent fasting such as energy, vitamin, mineral, and protein deficiencies, as well as the risk of disordered eating/eating disorders, should be considered before adopting this way of eating.

A registered dietitian can help you evaluate the benefits and drawbacks of intermittent fasting based on your health goals and history. If you choose to proceed, they will provide guidance to safely incorporate the diet plan. Finally, a dietitian will assist with customizing meals to increase satiety, which will enhance the sustainability of your fasting schedule.

Have we sparked your curiosity? Keep reading to learn what intermittent fasting (or IF) entails, what the research says, and whether you should (or should not ) give it a try. 

What is Intermittent Fasting?

Intermittent fasting is a dietary approach that focuses on when you eat rather than what you eat. Put simply, individuals alternate between periods of eating and periods of fasting. The theory behind this method is that your body undergoes metabolic changes during fasting periods. Insulin levels drop, promoting fat burning, and human growth hormone increases, aiding muscle gain and fat loss. Additionally, cellular repair processes are enhanced, and there’s improved regulation of blood sugar levels and inflammation. Supporters say that these changes can support weight management, improve metabolic health, and even extend longevity. 

Fasting periods vary, as intermittent fasting is actually not a single diet but an umbrella term for several different fasting regimens. The three most popular approaches are alternate-day fasting, the 5:2 diet, and time-restricted eating (also called time-restricted feeding).

The alternate-day fasting approach (ADF)

The alternate-Day Fasting (ADF) regimen goes back and forth between a fasting day and an unrestricted day. The non-fasting day is known as an ad libitum eating day (eating as much as you want and stopping when you’re full — aka mindful eating). 

There are two primary variations of alternate-day fasting: zero-calorie ADF and modified alternate-day fasting (MADF). In the zero-calorie regimen, no foods or caloric beverages are consumed on fasting days. In contrast, the MADF regimen allows for a caloric intake of 20% to 30% normal consumption on fasting days. 

The 5:2 approach

This method confines fasting to just two days per week (hence the name). Individuals eat their usual diet five days out of the week, then significantly limit intake to somewhere around 500 total calories on two (consecutive or nonconsecutive) days. 

A variation on 5:2 is called the Eat Stop Eat method, where individuals consume zero calories for one or two 24-hour fasting periods per week.

The time-restricted eating approach (TRE)

Time-restricted eating (TRE) is a popular version of intermittent fasting where individuals fast for somewhere around 14 to 16 hours daily and eat freely within a 4- to 10-hour window. The TRE regimen is highly variable, with fasting windows ranging from 12 to 21 hours per day. For example, the “Warrior Diet” is a spin on intermittent fasting that generally limits food consumption to four hours a day in the evening. Unlike the 5:2 diet and alternate-day fasting, time-restricted eating emphasizes a consistent daily eating window rather than energy restriction, aiming to achieve other potential health benefits.

What the Research Says About Intermittent Fasting

Some studies indicate that intermittent fasting can aid in weight loss, improve metabolic health, reduce body fat, and enhance brain function. In addition, research shows reductions in blood sugar levels, insulin resistance, and inflammation, which are key factors in preventing chronic disease. Finally, reviewers find that IF may promote longevity by triggering cellular repair processes and boosting human growth hormone levels. 

Proceed with caution, however, as this research has several limitations. Self-reported dietary intake, commonly used in these studies, can introduce inaccuracies that affect data reliability. Most studies are short-term, typically under a year, limiting the understanding of long-term health effects and sustainability. Additionally, there is a lack of diversity in participant demographics such as age, gender, ethnicity, and health status. This seriously constrains the generalizability of findings. 

The variability in fasting protocols (e.g. ADF, 5:2, TRE) also complicates comparisons and general conclusions about the efficacy and safety of intermittent fasting. Few studies consider the nutritional quality of diets during eating windows, which can significantly impact health outcomes. Moreover, there is a lack of long-term data. Most studies do not follow participants beyond a short period. 

These limitations highlight the need for more comprehensive, long-term research to fully understand the health implications of intermittent fasting.

Benefits of Intermittent Fasting

Can intermittent fasting be the key to better health for the right person? Let’s break down some of the potential benefits identified by researchers so far. 

Intermittent fasting for weight loss and fat reduction  

There is evidence that the three primary forms of intermittent fasting—alternate-day fasting (ADF), the 5:2 diet, and time-restricted eating (TRE)—are effective weight-loss strategies, leading to body weight reductions of 1% to 13% over periods ranging from 2 to 52 weeks.

However, when compared to caloric energy restriction, longer-term trials and other studies show no significant differences.

Results from a recent systematic review and meta-analysis published in the journal Obesity found that alternate-day fasting/modified ADF had the highest efficacy for weight loss compared with the 5:2 diet and time‐restricted eating. ADF/MADF showed the highest range of weight loss from 0.77% to 12.97% over 3 to 26 weeks as compared with the other regimens. The 5:2 diet produced weight loss ranging from 1.7% to 7.97%, whereas TRE ranged from 0.95% to 8.60% body weight loss.

However, the authors also concluded that more research is needed to determine how successful people are at sticking to IF versus traditional calorie restriction (CER).

Studies indicate that most people find it harder to maintain intermittent fasting after 3 months. This means that those attempting longer-term fasting protocols often struggle to adhere to the plan. In general, adherence to any weight-loss regimen (including IF) tends to decline after 1 to 4 months.

Currently, most of the research on IF and weight loss is limited to short-term studies with small sample sizes. Additionally, differences in meal timing, fasting duration, overall caloric intake, and background diet vary widely among studies, making it hard to confirm study findings.

If you’re on the fence, know that research shows other healthy diets (think: the Mediterranean diet , a well-rounded plant-based diet) are just as effective for weight loss as intermittent fasting — and they don’t (all) require strict food rules. Something to consider. 

Intermittent fasting to improve metabolic health

What happens to energy metabolism during fasting? When you begin fasting, your body first uses stored glucose (glycogen) from the liver and muscles for energy, a phase known as glycogenolysis. This lasts about 12-24 hours. Once glycogen is depleted, the body switches to creating glucose from non-carbohydrate sources like proteins, in a process called gluconeogenesis. As fasting continues, the body starts burning fat for energy, known as fat oxidation. The liver converts fatty acids into ketones, which serve as an efficient energy source for the brain and other organs. 

This switch to fat burning and ketone production, called ketogenesis, is crucial to the health benefits of intermittent fasting. Ever heard of the ketogenic diet ? This is exactly that process: ketosis.

This metabolic switch is thought to improve insulin sensitivity, reduce inflammation, and promote weight loss. Fasting also triggers a cellular cleanup process called autophagy, which removes damaged cells and proteins, potentially contributing to better overall health.

Potential benefits for disease prevention and longevity

There’s evidence that intermittent fasting may bolster the body’s stress response by forcing cells to be more adaptive. This phenomenon harkens back to when our ancestors regularly experienced periods of starvation. As a result, cells became more adaptive, revving up their antioxidant activity and DNA repair and decreasing inflammation. 

 Due to these potential benefits, IF has been studied for its potential to prevent and manage conditions like cardiovascular disease, type 2 diabetes, cancer, and Alzheimer’s disease.

The evidence on whether intermittent fasting has a clinically beneficial effect on glucose and lipid metabolism, cancer, or Alzheimer’s is still inconclusive. 

Intermittent fasting and Alzheimer’s — more research needed

One recent study suggests that intermittent fasting for 12–24 hours might help reduce the risk of Alzheimer’s disease pathology and its clinical manifestation of dementia. However, most current research in this area is based on animal studies. There are limited human trials on the effects of intermittent fasting on cognitive function and dementia. This is most likely due to the challenges in maintaining a fasting regimen and ensuring trial adherence amongst prospective participants.

Intermittent fasting is not recommended for those with cancer

The impact of intermittent fasting (IF) on human cancer incidence and prognosis is still unclear due to a lack of high-quality randomized clinical trials. Early studies indicate that prolonged fasting might be safe for some cancer patients and could reduce chemotherapy-related toxicity and tumor growth. However, more research is needed to understand the risks and benefits of fasting for cancer patients. Therefore, it is not recommended for those undergoing active cancer treatment to try IF outside of clinical trials. While IF may help with weight management and potentially offer cancer prevention benefits, its direct effects on cancer-related pathways remain unknown. 

Other health outcomes from intermittent fasting

We don’t yet know the effects of intermittent fasting on major health outcomes like death, heart attacks, and heart failure. This is simply due to insufficient data. Some studies suggest that IF can help reduce weight compared to unrestricted eating, making it as effective an approach as continuous calorie restriction. However, weight changes are often small and not clinically significant in the short term. The quality of the current evidence is low, leaving many uncertainties. More research is needed to determine which patients might benefit from IF and to understand its long-term effects on overall mortality and heart disease .

Who Should Avoid Intermittent Fasting?

There are a few groups that definitely need to steer clear of IF: individuals with advanced type 2 diabetes, pregnant or breastfeeding women, and those with a history of disordered eating. People prone to stress and anxiety may also want to avoid intermittent fasting.

If you have type 2 diabetes

Diabetics should eat at regular intervals to maintain stable blood sugar levels. Fasting periods can lead to hypoglycemia (dangerously low blood sugar) if medications such as insulin or sulfonylureas are not adjusted appropriately. Additionally, extended fasting may result in hyperglycemia (high blood sugar) if the body starts breaking down muscle tissue for energy. This can complicate the management of diabetes and lead to other health issues. 

If you are pregnant or breastfeeding 

Pregnancy and breastfeeding require a steady intake of calories and nutrients to support the growth and development of the baby and to maintain the health and well-being of the mother. Intermittent fasting can lead to a calorie deficit and nutrient deprivation, which may affect milk production, energy levels, and overall nutritional status. Furthermore, fasting can cause fluctuations in blood sugar levels, which can be detrimental to both the mother and the baby. It’s crucial for pregnant and breastfeeding individuals to have a balanced healthy eating pattern with regular meals to ensure they are meeting their increased nutritional requirements. 

If you have a history of disordered eating

When it comes to individuals with a history of disordered eating, IF can be dangerous territory. Why? The restrictive nature of intermittent fasting diets can lead to a preoccupation with food, rigid control over eating times, and feelings of guilt or anxiety around meals, all of which can be harmful for those recovering from or prone to eating disorders. Additionally, the fasting periods can contribute to binge eating during eating windows, creating a cycle of restriction and overconsumption. Plus, fasting can mess with natural hunger and satiety cues. For individuals with a history of disordered eating, a more flexible and balanced approach to healthy eating, focusing on regular, nutritious meals, is generally safer and more supportive of long-term recovery and mental health. 

If you are prone to stress and anxiety

Fasting increases levels of the stress hormone cortisol in the body. This makes sense: not eating for an extended period of time eventually triggers the body’s stress response. If you’re someone who already struggles with anxiety, elevated cortisol levels related to IF may further exacerbate physiological symptoms of stress, like rapid heart rate and breathing, high blood pressure, and high blood sugar. Additionally, prolonged fasting periods can lead to irritability, mood swings, and difficulty concentrating, further aggravating stress and anxiety.

Even if you don’t fall into any of the above categories, IF still may not be for you if it doesn’t match your lifestyle. For instance, if you’re someone who lives for breakfast, there’s no reason to subject yourself to time restricted eating. Similarly, if you know you get light-headed when you haven’t eaten in a few hours, fasting may pose a serious threat to your health. If that’s the case, consider IF “not worth it” and consult with a registered dietitian to find a healthy meal plan that works better for your body. 

How to Start Intermittent Fasting Safely

Choose the right type of fasting for your lifestyle.

If you want to try intermittent fasting, it’s important to find a method that aligns with your lifestyle and health needs. Start by considering your daily schedule, work commitments, and personal preferences. Time-restricted eating, where you fast for 14 to 16 hours daily and eat during an 8- to 10-hour window, is popular for its flexibility and ease of integration into most routines. If you prefer a less frequent fasting pattern with majority non-fasting days, the 5:2 method might be a better fit. If alternate-day fasting appeals to you, just consider whether you will be able to maintain your normal activity levels on restricted eating days. 

Adjust gradually and listen to your body

Begin by slowly increasing the duration of your fasting periods, allowing your body to adapt to each new eating pattern without feeling overwhelmed. For instance, if you choose alternate-day fasting, you might start by incorporating one fasting day per week and gradually increase it to every other day. Listen to your body’s cues for hunger and fullness, and don’t disregard signs of fatigue, irritability, or excessive hunger. If you experience any discomfort or adverse effects, consider adjusting your approach. 

Maintain a balanced diet during eating windows

There’s a misconception about IF that non-fasting or ad libitum periods give carte blanche to eat endless unhealthy foods. “Ad libitum” is Latin for “to one’s pleasure.” When referring to eating, this phrase means you can eat as much and as often as desired, simply stopping when you’re full. But it’s important to note that the positive (or negative) health effects of specific foods will still impact you even if you’re practicing periods of intermittent fasting. 

Maintaining a balanced diet during your eating windows is crucial for the success and safety of an intermittent fasting eating plan. Focus on consuming a variety of nutrient-dense foods that provide essential vitamins, minerals, and energy. Incorporate plenty of fruits and vegetables, whole grains, lean proteins, and healthy fats into your meals. A balanced approach will ensure that your body receives the necessary nutrients to function optimally on both fasting and non-fasting days. This will support sustained energy levels and promote overall well-being. 

Lastly, it’s essential to stay hydrated — especially when fasting. Make sure you drink plenty of water! 

Consult with your doctor and work with a registered dietitian 

Intermittent fasting is not for everyone. Before starting an IF program, check with your doctor to identify any underlying health conditions or medications that fasting might affect. Then, meet with a registered dietitian to create a balanced, nutritious, and sustainable intermittent fasting meal plan. Your RD will also monitor your progress and make necessary adjustments to ensure you’re meeting health goals without compromising your well-being. 

How Registered Dietitians Can Help With Intermittent Fasting

Since you will not be receiving essential nutrients through food during fasting windows, it’s important to ensure maximum nutrition during non-fasting times. Registered dietitians have extensive knowledge of various eating plans, and they understand the science behind the different modes of intermittent fasting. A registered dietitian will help you determine what to eat when you’re not fasting to promote satiety and overall health.

An RD also has the experience to predict potential pitfalls, and can help you adjust your fasting plan before you experience negative impacts. One common issue is dehydration. A registered dietitian can give you hydration tips and teach you what to look out for to avoid becoming dehydrated. 

As part of your care plan, a registered dietitian will also share sample recipes and food prep tips that are personalized to your fasting protocol, lifestyle, and tastes.

Finally, a registered dietitian can also advise you on supplements and vitamins to support intermittent fasting as needed.

Frequently asked questions about intermittent fasting

Next, we’ll tackle some of the intermittent fasting questions we hear most often in our nutrition practice. Note that these are generalized responses. Consult with your registered dietitian for more personalized advice!

Can I drink coffee/tea during fasting periods?

You can drink coffee and tea during fasting periods, but opt for black coffee or plain tea to avoid breaking your fast. Avoid adding sugar, cream, or any high-calorie additives. These can interfere with the fasting process by triggering an insulin response. If you prefer a little flavor, try adding a slice of lemon or a dash of cinnamon to your tea. Additionally, be mindful of your caffeine intake, as excessive amounts can lead to dehydration and poor sleep hygiene. 

What foods should I avoid during intermittent fasting?

Balance is key. Make the most of your eating windows by focusing on nutrient-dense foods. You can still incorporate less nutritious treats into your regimen, as long as you consume them in moderation. Steer clear of excessive high-sugar and highly processed foods, as they can cause spikes in blood sugar levels and lead to cravings and energy crashes. Additionally, you may want to limit your intake of refined carbohydrates like white bread and pastries, which offer little nutritional value. Instead, prioritize whole foods that provide sustained energy and essential nutrients, such as fruits, vegetables, lean proteins, whole grains, and healthy fats. 

How does intermittent fasting affect exercise performance?

Intermittent fasting can influence exercise performance in various ways, with effects differing from person to person. For some, fasting may enhance fat burning and improve metabolic efficiency, which can be beneficial for endurance activities. However, exercising on an empty stomach might also lead to decreased energy levels, reduced strength, and lower overall performance, particularly for high-intensity or resistance training workouts. It’s crucial to listen to your body and adjust your exercise routine accordingly. Some individuals find it helpful to schedule their workouts during their eating windows to ensure they have adequate fuel and recovery nutrients. 

What are some of the side effects of intermittent fasting?

Common side effects of intermittent fasting include hunger, fatigue, irritability, and difficulty concentrating. Some people may also experience headaches, dizziness, or digestive issues like constipation or bloating. These symptoms often subside as the body becomes accustomed to fasting. Long-term or overly restrictive fasting can lead to nutrient deficiencies, reduced muscle mass, or metabolic slowdown. There is also a risk of developing a psychological condition such as binge eating disorder , which can be triggered or exacerbated by time restricted eating.

It’s important to monitor your health with a medical provider before and during intermittent fasting to navigate these potential side effects. 

What if I feel extremely hungry or weak?

Experiencing extreme hunger or weakness during intermittent fasting is a signal that your body needs nourishment and energy. It’s important to listen to these cues and address them appropriately. It may be beneficial to adjust your fasting schedule or the types of foods you’re eating on non fasting days. Incorporating more nutrient-dense, high-fiber, and protein-rich foods can help keep you fuller for longer to maintain steady energy levels. Don’t hesitate to break your fast if necessary; your health and well-being are the top priorities. 

Personalized Guidance for Successful Intermittent Fasting

Initial research into intermittent fasting shows that it could result in improved metabolic health, enhanced cellular repair, and weight loss for the right candidate. But there is also a risk of side effects, including malnutrition and disordered eating. That’s where professional support and guidance comes in. 

Partner with a registered dietitian to determine whether intermittent fasting is a safe and effective approach for your needs. Whatever you decide, your dietitian will help you develop a nutritious and satiating way of eating that supports your long-term goals. 

Any general advice posted on our blog, website, or application is intended for reference and educational purposes only and is not intended to replace or substitute for any professional medical advice, diagnosis, treatment, or other professional advice. If you have specific concerns or a situation arises in which you require medical advice, you should consult with an appropriately qualified and licensed medical services provider.

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Is 'intermittent fasting' a shortcut to performance gains?

With time restricted eating an increasingly popular approach, Hannah Reynolds delved into the research, and tested the theory for herself

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In our 'Will It Work?' series, Sports Science expert Hannah Reynolds investigates common fitness hacks, to determine if they're really any good for the time crunched athlete.  

Intermittent fasting (IF) is an eating pattern where individuals cycle between periods of eating and fasting. Unlike traditional dieting which focuses on what to eat, IF focuses on when to eat. 

Common methods of IF include the 16:8 method (16-hour fast with an 8-hour eating window), the 5:2 approach (eating normally for 5 days and limiting calories to 500-600 on 2 non-consecutive days), and the eat-stop-eat method (24-hour fasts once or twice a week).

People choose intermittent fasting for various reasons. Weight loss is a primary motivation as fasting can help reduce calorie intake and improve metabolic health. Supporters of IF say that limiting eating periods may aid in reducing insulin levels, promoting fat burning and supporting weight management. Additionally, some find IF easier to stick to than other calorie-restricted diets as it doesn’t necessarily restrict what can be eaten, only when.

Aside from weight loss, IF has also been linked to health benefits like improved heart health, enhanced brain function, and increased longevity. Preliminary research has suggested that intermittent fasting can reduce inflammation, improve cholesterol levels, and enhance the body's ability to manage blood sugar. While more studies are needed, the potential health benefits combined with the simplicity of the approach make IF an attractive option for many.

Expert opinions on intermittent fasting

One study had athletes packing all of their eating in between the hours of 10am and 6pm

Research from as early as 2009 in the Journal of Strength and Conditioning showed some interesting results; overnight fasting and calorie restriction improved cyclists power to weight ratio without compromising their endurance performance. Their body composition improved significantly, and their overall weight, fat weight, and body fat percentage decreased while lean mass was maintained. 

More recently, 2020 research published in the Journal of the International Society of Sports Nutrition revealed that an 8-hour feeding window elicits weight loss, improves body composition and increases peak power output and body weight in elite cyclists. 

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Time restricted eating could also be beneficial for reducing inflammation and may have a protective effect on some components of the immune system. Researchers concluded that time restricted eating could be considered as a useful component of a periodised nutrition plan in endurance athletes. 

However, a few things should be noted; the test period was only four weeks and the athletes ate 100% of their daily energy needs in an eight hour time window from 10:00am to 6:00 pm, under the supervision of a team dietitian. The athletes didn’t eat less, they just ate within a restricted time window. Furthermore, the study was conducted during the winter pre-competition season so most of the training consisted of long rides at a steady state mild to medium pace and all the training took place within the feeding time window 10am-6pm so was not done in a fasted state.  

Whilst IF has many supporters, it's an approach that comes with words of caution.

Renee McGregor , a sports dietitian specialising in eating disorders says that intermittent fasting is not a practice that she would ever recommend for anyone trying to improve their performance, “Be careful in how you interpret the research,” she warns, “there are no performance benefits to doing intermittent fasting. A lot of the studies are done on a particular outcome, for example weight loss, rather than a long-term effect on performance.” 

Fasting may prompt unhealthy eating patterns “we know that if you don’t fuel well in the morning when you are training, your glycaemic control later on in the day is affected,” simply put if you fast early on in the day you are more likely to make poor food choices or even binge eat at other times, “the human body is biologically biased to always achieve energy balance, If you are doing a lot of exercise you are going to be hungry.” One of the many concerns with intermittent fasting particularly over longer periods of time, is the effect on hormone balance, “we know that if oestrogen for example goes too low especially for women, it can have serious negative effects on the cardiovascular system. You may reach a point where your cardio training is no longer having a positive effect on performance.” 

Intermittent fasting can lead to disordered eating , an area that McGregor specialises in “obsessive behaviour can lead to problematic outcomes,” she cautions. McGregor is reluctant to encourage any athlete to try intermittent fasting “we have to be careful that it isn’t setting you up to fall into bad habits. Developing lower metabolic efficiency or eating to excess when you do allow yourself to eat. Potentially you can set yourself up to fail, that is why I am particularly cautious about it and I would never suggest it. However, there are some situations where it might be acceptable.” As with the research mentioned above she suggests that IF should be done carefully with some supervision and that your training is done fuelled,  “if you are going to go down this road I would shift everything so you are not training in a fasted state. Ensure that you have some sort of monitoring to check that your hormone levels are working and remain very mindful of how your performance is going.” 

Pros of intermittent fasting

• Improved Fat Adaptation: Some research suggests IF may help cyclists become more efficient at burning fat for fuel, which can be particularly useful for endurance events
• Weight Management: IF can be an effective way to reduce body fat, potentially improving power-to-weight ratio—a critical factor in cycling performance – as long as you manage your nutrient intake around fasting periods
• Metabolic Health: IF has been shown to improve insulin sensitivity and blood sugar control, which can be beneficial for overall metabolic health and energy regulation during rides.
• Simplified Meal Planning: IF requires will power during fasts and good nutrition the rest of the time meaning no counting calories, weighing portions or becoming fixated on food

Cons of intermittent fasting

• Energy Levels: Fasting periods might lead to low energy levels, which can negatively affect performance and recovery
• Nutrient Intake: Restricting eating windows could make it challenging to consume all the necessary nutrients and calories needed for optimal performance and recovery
• Muscle Loss: There’s a risk of muscle breakdown if calorie intake is too low, especially during prolonged fasts or if nutrition isn't carefully managed
• Gastrointestinal Issues: Eating larger meals in a shorter time frame can lead to gastrointestinal discomfort, which can be particularly problematic before or during rides

I tried it... 

Hannah Reynolds tested intermittent fasting

Having read up on the reported benefits, and received a warning to be cautious from McGregor, I tentatively experimented with IF.

I started with a simple 16:8 – eating 8 hours a day and nothing the rest of the time as per the second piece of research above. This model was really easy, breakfast at 10.30am and dinner at 6.30pm. Just restricting eating hours in this way immediately removed the option of cheese and biscuits late at night or having a mid-morning coffee and croissant. That alone was enough to make a noticeable difference! But that could have been achieved anyway without calling it ‘fasting’. 

The next level is to have two fast days with just 500 calories on those days, and this was considerably harder. Herbal teas, water and lots of salad helped the process. The most noticeable thing is that the day after fasting I felt lighter, healthier and made better food choices, there was no compensatory binge. However, it remains to be seen if I'd continue to see benefits over a longer period. 

Overall, I think this method would work for me as long as I don’t become too fixated and am prepared to put good nutrition before fasting on the days when exercise demands it. 

The bottom line on intermittent fasting

Intermittent fasting is a tool to handle with caution. It can suit some people very well but others will find it makes them much less able to train effectively so their performance and more crucially well-being will suffer. 

Time restricted eating, consuming all the nutrients and energy you need in an 8-hour window that includes your training and immediate recovery time, may be a healthier way to think about this method by removing the emphasis on ‘fasting’. It is essential to time eating windows around training sessions to ensure sufficient energy and nutrients for both performance and recovery. Shorter fasting periods are easy to achieve and may reduce unhealthy habits like late night snacking, while conversely training fasted or longer fasts could lead to binge eating or at the very least bad food choices which will be over all detrimental to your progression. 

If you are tempted to try intermittent fasting focus on the why - if it is to improve your performance as a cyclist question if this method will allow you to achieve that.  

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Hannah Reynolds interest in cycling began while studying for a degree in Sports Science at the University College Chichester and surrounded by elite level cyclists. She is now undertaking a PhD at Sheffield Hallam University investigating the use of e-bikes by older people. 

A committed dabbler whose passion outweighed her talent Reynolds has competed across all disciplines of cycling bar BMX. In the very distant past she has been south-east road race champion, southern cyclo-cross champion and finished third in the European 24hr Solo mountain-bike champs in 2011. She was also the Fitness Editor of Cycling Weekly for 15 years. 

Hannah Reynolds is author of several cycling books,  France-en-Velo  a guide to the ultimate 1000 mile cycle route from the Channel to Med;  Britain's Best Bike Ride. LEJOG1000 ; A 1000 mile journey from Land's End to John o' Groats and  1001 Cycling Tips . 

Are you putting obstacles in the way of your own progress? Josephine Perry examines nine common self-sabotaging behaviours and how to quit them

By Josephine Perry Published 27 July 24

Get all the information you need to watch the action of the men's and women's Olympic cycling time trials today at Paris 2024

By Cat Glowinski Published 26 July 24

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Two Diets Linked to Improved Cognition, Slowed Brain Aging

Pauline Anderson

July 25, 2024

An intermittent fasting (IF) diet and a standard healthy living (HL) diet focused on healthy foods both lead to weight loss, reduced insulin resistance (IR), and slowed brain aging in older overweight adults with IR, new research showed. However, neither diet has an effect on Alzheimer's disease (AD) biomarkers.

Although investigators found both diets were beneficial, some outcomes were more robust with the IF diet.

"The study provides a blueprint for assessing brain effects of dietary interventions and motivates further research on intermittent fasting and continuous diets for brain health optimization," investigators led by Dimitrios Kapogiannis, MD, chief, human neuroscience section, National Institute on Aging, and adjunct associate professor of neurology, The Johns Hopkins University School of Medicine, wrote.

The findings were published online on June 19 in Cell Metabolism .

Cognitive Outcomes

The prevalence of IR — reduced cellular sensitivity to insulin that's a hallmark of type 2 diabetes — increases with age and obesity adding to an increased risk for accelerated brain aging as well as AD and related dementias (ADRD) in older adults who have overweight.

Studies reported healthy diets promote overall health, but it's unclear whether, and to what extent, they improve brain health beyond general health enhancement.

Researchers used multiple brain and cognitive measures to assess dietary effects on brain health, including peripherally harvested neuron-derived extracellular vesicles (NDEVs) to probe neuronal insulin signaling; MRI to investigate the pace of brain aging; magnetic resonance spectroscopy (MRS) to measure brain glucose, metabolites, and neurotransmitters; and NDEVs and cerebrospinal fluid to derive biomarkers for AD/ADRD.

The study included 40 cognitively intact overweight participants with IR, mean age 63.2 years, 60% women, and 62.5% Caucasian. Their mean body weight was 97.1 kg and mean body mass index (BMI) was 34.4 kg/m 2 .

Participants were randomly assigned to 8 weeks of an IF diet or a HL diet that emphasizes fruits, vegetables, whole grains, lean proteins, and low-fat dairy and limits added sugars, saturated fats, and sodium.

The IF diet involved following the HL diet for 5 days per week and restricting calories to a quarter of the recommended daily intake for 2 consecutive days.

Both diets reduced neuronal IR and had comparable effects in improving insulin signaling biomarkers in NDEVs, reducing brain glucose on MRS, and improving blood biomarkers of carbohydrate and lipid metabolism.

Using MRI, researchers also assessed brain age, an indication of whether the brain appears older or younger than an individual's chronological age. There was a decrease of 2.63 years with the IF diet ( P = .05) and 2.42 years with the HL diet ( P < .001) in the anterior cingulate and ventromedial prefrontal cortex.

Both diets improved executive function and memory, with those following the IF diet benefiting more in strategic planning, switching between two cognitively demanding tasks, cued recall, and other areas.

Hypothesis-Generating Research

AD biomarkers including amyloid beta 42 (Aβ42), Aβ40, and plasma phosphorylated-tau181 did not change with either diet, a finding that investigators speculated may be due to the short duration of the study. Light-chain neurofilaments increased across groups with no differences between the diets.

In other findings, BMI decreased by 1.41 kg/m 2 with the IF diet and by 0.80 kg/m 2 with the HL diet, and a similar pattern was observed for weight. Waist circumference decreased in both groups with no significant differences between diets.

An exploratory analysis showed executive function improved with the IF diet but not with the HL diet in women, whereas it improved with both diets in men. BMI and apolipoprotein E and SLC16A7 genotypes also modulated diet effects.

Both diets were well tolerated. The most frequent adverse events were gastrointestinal and occurred only with the IF diet.

The authors noted the findings are preliminary and results are hypothesis generating. Study limitations included the study's short duration and its power to detect anything other than large to moderate effect size changes and differences between the diets. Researchers also didn't acquire data on dietary intake, so lapses in adherence can't be excluded. However, the large decreases in BMI, weight, and waist circumference with both diets indicated high adherence.

The study was supported by the National Institutes of Health's National Institute on Aging. The authors reported no competing interests.

Send comments and news tips to [email protected] .

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What is 16:8 intermittent fasting and can it help you lose weight?

Intermittent fasting is a popular approach to dieting that focuses less on what you eat and more on when, but it isn’t one size fits all. There several versions of the eating plan, with one of the more well-known options being the 16:8 intermittent fasting method, which many people use to lose weight.

But first things first: Time-restricted eating isn’t about changing your diet or counting calories .

Instead, intermittent fasting requires you to fast for a period of time each day or week, per the Mayo Clinic . And because of the shorter eating window, by the end of the day or a week, you will likely be in a calorie deficit.

But how and when you fast can vary. Some people create and adhere to their own time-restricted eating pattern by stopping eating by 6:00 p.m., for example. If you're not sure where to start, there are four common methods for intermittent fasting: the 16:8 method, the 5:2 method, alternating the days you’ll eat and fast and time-restrictive intermittent fasting.

Here's what to know about the 16:8 intermittent fasting method in particular.

What are the rules for 16:8 intermittent fasting?

The main rule of the 16:8 intermittent fasting plan is fasting for 16 hours of the day and eating normally for eight.

It's not a diet, so unless you have individual dietary restrictions, you can eat whatever you want within the eight-hour time frame. But the plan will work best for weight loss if you are already making smart, nutrient-rich choices, said NBC News health and nutrition editor Madelyn Fernstrom, Ph.D.

For some people, restricting the amount of time they have to eat in a day naturally limits the number of calories they consume and therefore contributes to weight loss. How you go about fasting is up to you, but those following the 16:8 method will typically only drink water during their 16-hour fast while others will make exceptions for sugar-free beverages, says Dr. Deena Adimoolam, a specialist in endocrinology and obesity medicine.

It might be better referred to as "intermittent eating," because it's not about deprivation, but rather about "boosting mindful eating and a new relationship with food," Fernstrom added.

Can you lose weight with 16:8 intermittent fasting?

The research on whether 16:8 intermittent fasting is good for weight loss is mixed.

A small 2018 study found people with obesity who followed the 16:8 fasting regimen for three months lost almost 3% of their body weight and lowered their blood pressure without feeling hungry or deprived.

The participants ended up eating 350 fewer calories a day compared to a control group simply because they couldn't squeeze in their normal food intake between 10 a.m. to 6 p.m., the prescribed eating window in the study, co-author Krista Varady, Ph.D., a professor of nutrition at the University of Illinois, Chicago, told TODAY.com. She has been studying fasting for 20 years.

Varady's latest study , published in June 2023, showed time-restricted eating without calorie counting was as effective as limiting calories and tracking them for weight loss. For the trial, people with obesity were asked either to eat only between noon and 8 p.m., or to eat whenever they wanted but count calories and reduce the amount of food they normally ate by 25%. They followed those routines for six months.

Both groups generally maintained the weight loss after their diets ended and lost 5% of their body weight over the course of a year, Varady told NBC News.

A 2020 systematic review of 27 studies that involved different kinds of intermittent fasting, including the 16:8 plan, found participants lost between 0.8% to 13.0% of their initial weight with no serious adverse events. The authors concluded intermittent fasting "shows promise" for the treatment of obesity.

But research presented at the American Heart Association's Scientific Sessions in 2020 found obese adults who ate most of their calories by 1 p.m. for three months didn't lose more weight than those who followed a more typical eating pattern, including eating a big meal after 5 p.m.

"The bottom line is that how many calories you take in is really much more important than when you eat, and that when you eat probably doesn't impact your weight," Dr. Nisa Maruthur, lead author of the AHA research and associate professor of medicine at Johns Hopkins University in Baltimore, previously told TODAY.com.

And the results of a 2023 study on the timing of meals, published in the Journal of the American Heart Association, "did not support the use of time‐restricted eating as a strategy for long‐term weight loss," researchers wrote. The timing of meals was less important than the amount of food a person ate, they noted .

Tips to start 16:8 intermittent fasting

If you're ready to try 16:8 intermittent fasting, Varady has some tips to make sure you do it in a way that is healthy and works with your lifestyle.

Pick a time window that works for you.

Experts advise picking an eating window that lets you finish your meals fairly early, such as 10 a.m. to 6 p.m. or earlier, because the body is less efficient at processing sugar as the day goes by.

In an "absolute ideal world," people would eat breakfast, take in most of their calories during the first part of the day, have a very light dinner — if any at all — and then fast for the rest of the evening, Dr. Susan Cheng, a professor of cardiology and the director of public health research in the Smidt Heart Institute at Cedars-Sinai in Los Angeles, told TODAY.com.

"For many of my patients, there are certain times of the day when they consume unnecessary calories - what I call "mindless calories," explains Adimoolam. "Those extra calories are typically after dinner when mindless snacking and drinking occurs while watching television and relaxing after a long day." She recommends fasting after dinner.

Other experts agree. Dr. Reshmi Srinath, endocrinologist and director of obesity medicine at Mount Sinai, says she typically recommends her patients stop eating by 8:30 p.m. to avoid late-night snacking.

But, that won't work for everyone. So it's important to pick a window of time that works for your schedule. If you're a very early riser, for example, it may be difficult to wait until noon to eat.

Exercise before you eat.

Most people get hungry about half an hour after they finish working out and may find it too hard to stick to their plan if they can’t eat anything at all afterward, Varady notes. That's why it's important to exercise before you eat.

If you’re on the 16:8 plan, exercise before your eating window, or make sure to finish your workout at least 90 minutes before your eating window ends for the day.

Get enough rest.

Fasting for 16 hours may sound tough, but if you're getting the recommended seven or more hours of sleep per night, you'll be asleep for about half of it.

Drink black coffee.

It's common to feel low energy at times when following this eating plan. Drinking black coffee can improve concentration and energy, and it has no calories in it, Varady said.

Take a deep breath.

Mindfulness and a bit of meditation can go a long way in helping to restore your energy during your fasting period.

Avoid snacking.

Many people are used to grazing and nibbling all day long, but there's no snacking during the fasting periods of intermittent fasting.

Here are some ways to avoid getting "hangry":

• Eat high-fiber foods , such as nuts, beans, fruits and vegetables and high-protein foods , including meat, fish, tofu or nuts, during your eating window, Varady advised. Chewing high-fiber gummies can also help.
• Drink lots of water . People tend to think they're hungry when they are really just thirsty, Varady said.
• Opt for certain teas, like cinnamon or licorice herbal teas. These beverages may have appetite-suppressing effects, Varady noted.

Watch less TV.

“I know this sounds strange, but while you are watching TV, you are bombarded with dozens of ads for food. This can make you feel hungry, when in actuality you are not hungry at all,” Varady said.

Turn to peppermint.

Use peppermint to defuse cravings . Inhaling a peppermint scent every two hours helped people defuse cravings and eat fewer calories, a study found. The exact reasons are unclear.

Avoid drinking too much alcohol.

Don't drink any alcohol during your fasting window since it's high in calories and has no nutritional value, Varady advised. During non-fasting periods, women should limit their alcohol intake to one drink a day; men shouldn't have more than two.

Develop ways to get your mind off food.

If you can't seem to stop thinking about food, you might consider mechanisms that will help you redirect your focus. Adimoolam recommends listening to music, taking a walk or drinking some water.

If you have a medical condition, talk to your doctor about intermittent fasting first.

There are certain medical conditions for which intermittent fasting isn't suitable, says Adimoolam. So, she recommends talking to your doctor about your plan incorporate fasting into your day. You might find another dietary regimen is actually better for you and your health.

Go easy on yourself.

There are days when you won't feel well, Srinath points out. "Listen to your body," she says. "If there's a day when you're not feeling great, you can skip a day." Instead, focus on fueling your body and feeling your best.

Don't give up too quickly.

If weight loss is your goal, it might take some time to notice a difference in your body, says Srinath. "If you don't see results within two months," she says, "try seeing a weight loss specialist." They can help you adjust your fasting timeline or help you come up with different eating plan that might suit you better. If you don't feel well while intermittent fasting, however, don't push past those feelings of discomfort to make it to the two-month mark.

Health benefits of 16:8 intermittent fasting

Weight loss or not, there appear to be health benefits to intermittent fasting.

It may protect the heart by controlling inflammation, according to the American Heart Association .

"The idea is that if you eat all of your calories within a relatively fixed time window ... it's better because it allows your body to do this metabolic catch-up during a fasting state when you're not eating," Cheng explained. "I would say the jury is still out, but there is a lot of compelling evidence to suggest that is going to be favorable for cardiometabolic health."

Studies and clinical trials suggest intermittent fasting has "broad-spectrum benefits" for health problems such as obesity, diabetes, heart disease, cancer and neurologic disorders, according to a review of research in humans and animals published in 2019 in the New England Journal of Medicine.

The powerful health effects appear to come from the body shifting away from using sugar as its main source of energy and instead converting fat for fuel when a person's stomach is empty. When a person switches between a fed and fasted state, it stimulates responses that boost mental and physical performance, plus disease resistance, the authors wrote.

In addition, intermittent fasting can be easy to follow, provide daily structure and doesn’t require any calorie counting . It also reconnects people with true, biological hunger and makes it easier to

Does 16:8 fasting work for people with Type 2 diabetes?

Eating only within an eight-hour window can help people with Type 2 diabetes lose weight and manage their blood sugar, according to a study published in JAMA Network Open in October 2023.

The clinical trial involved 75 adults with Type 2 diabetes and obesity who were randomly divided into three groups for six months. One group could eat whatever and as much as they wanted but only between noon and 8 p.m. The second group was instructed to eat 25% fewer calories than normal, and the rest stuck to their usual eating routine.

The participants' weight and blood sugar levels were measured at baseline, and then regularly throughout the six-month trial.

"We found that the fasting group lost twice as much weight as (daily calorie counting), but both groups improved HbA1c, a key diabetes risk parameter, similarly," Varady, a co-author of the study, told TODAY.com.

HbA1c measures a person's average blood sugar levels over the past three months. It fell about 0.7% for both groups. The fasting group also lost about 10 pounds over six months on average, compared to less than 6 pounds for the calorie-counting group.

Eating fewer calories is commonly prescribed as the first line of defense in Type 2 diabetes treatment, but many patients struggle with it, so time-restricted eating may offer a "refreshing alternative," the paper noted.

There were no serious adverse events reported during the trial, so the study shows intermittent fasting is safe in this population group, Varady said. But she advised people with diabetes to always check with their doctors before starting time-restricted eating.

The findings need to be confirmed by larger trials with longer follow-up, the authors noted.

Intermittent fasting isn't for people with Type 1 diabetes who take insulin because it may result in unsafe levels of hypoglycemia, or low blood sugar, during the fasting period, Mark Mattson, Ph.D, a leading researcher on intermittent fasting and adjunct professor of neuroscience at Johns Hopkins University School of Medicine, said.

Other types of intermittent fasting

If 16:8 intermittent fasting doesn't feel right for you, here are some other approaches to consider.

This plan means incorporating two non-consecutive fast days into your week, then eating normally during the other days. To follow this plan, eat as you normally would five days a week and consume fewer than 600 calories two days a week.

Alternate-day intermittent fasting

Eat was you normally would one day, then fast by eating fewer than 600 calories the next — and repeat throughout the week.

18:6 method

This intermittent fasting strategy allows people to eat for six hours a day, usually between 8 a.m. and 2 p.m., and fast for 18 hours. Research has shown that it can curb appetite by decreasing levels of hunger hormones and increasing levels of satiety hormones.

How does intermittent fasting affect hormones?

As intermittent fasting has become more popular, concerns have emerged due to rat studies that it has effects on hormonal cycles and fertility — and those fears have been amplified by social media.

"There have been a couple of animal studies that I don't think are very translatable to humans," Varady, said. "But the second they're up on Instagram, everyone finds out about them."

A 2022 study in the journal Obesity investigated the impact of intermittent fasting on women’s hormones. Two groups of women followed time-restricted eating plans for eight weeks. In the end, the findings were reassuring, Dr. Reshmi Srinath, director of the Mount Sinai Weight and Metabolism Program, told TODAY. Hormone levels weren’t drastically disrupted.

In postmenopausal women, there was no change in their levels of estradiol, estrone or progesterone. The only hormone that changed significantly during the study period was dehydroepiandrosterone, also called DHEA, which helps the body make male and female sex hormones, according to Mayo Clinic . DHEA, which can naturally rise and fall with weight changes.

Both groups of women in the study saw a statistically significant decrease in DHEA levels over the eight weeks they were on the time-restricted eating plan. But Varady emphasized that, even with the drop, participants' DHEA levels were still within the normal range — and they didn't show any worrying side effects in other tests.

Drawbacks of 16:8 intermittent fasting

“A lot of people who try to switch to intermittent fasting don’t realize it takes a while to adapt,” Mattson noted. They may experience hunger and irritability at first, but these usually disappear within a month.

To reduce side effects of intermittent fasting, ease into it, the experts advise. Start with an eating window of 12 hours, then gradually reduce it to 10 and then eight over several months.

Another reported drawback of intermittent fasting is a lack of flexibility, according to a small pilot study from 2018 published in the Journal of Nutritional Science. "Fasting diets are difficult to follow and may not always be compatible with family and social life," lead researcher Dr. Jonathan Johnston said.

If you want to try intermittent fasting but don't want to be locked into one schedule, try fasting a few non-consecutive days a week with a few days of time-restricted feeding.

Many people also think that intermittent fasting promotes disordered eating. However, Varady said the research shows that, unlike many fad diets, intermittent fasting doesn’t lead to eating disorders or slow down a person’s metabolism, Varady said. A 2022 review of studies she co-authored found intermittent fasting is generally safe and produces few gastrointestinal, neurological, hormonal or metabolic adverse effects.

Long periods of fasting won't suit everyone, says Adimoolam. Stop if you experience symptoms like dizziness, lightheadedness, sweating, nausea, vomiting, brain fog, impaired memory, difficulty with concentration or fatigue. These could "be signs that your body needs food for energy and it's time to eat something."

Who should not try intermittent fasting?

Intermittent fasting, the 16:8 plan or otherwise, is not recommended for everyone. These groups include:

• Children or adolescents
• Women who are pregnant or lactating
• People with eating disorders
• Individuals who are underweight (have a body mass index below 18.5)
• People over the age of 70 because fasting may exacerbate muscle wasting in this population

Always check with your doctor or a dietitian before starting an intermittent fasting regimen.

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10 Amazing Benefits of Intermittent Fasting

The practice of fasting can lead to many metabolic changes within the body. These changes typically begin approximately three to five hours after eating, when the body enters a “post-absorptive” state – rather than the state of ongoing digestion, where eating frequent meals means the body is always involved in some sort of digestive activity.

Why should you practice intermittent fasting?

Whether you practice more long-term fasting for health reasons or spiritual reasons, most people will have to fast at some point for medical reasons. Patients undergoing surgery or other medical procedures that require a general anaesthetic will usually fast before the treatment, but fasting is also practised before several other medical tests, including cholesterol testing, blood glucose measuring, or a lipid panel. This enables doctors to achieve accurate results and establish a solid baseline to inform future testing, if necessary.

#1 Weight Loss

Instead of running on fuel from the food you just ate, fasting allows your body to tap into reserves – fat, which accumulates in the body to be burned whenever the food supply grows scarce. This results in a slow, steady weight loss that can be a huge benefit.

Since fasting is often incorporated as a lifestyle change instead of a temporary fix, this type of diet is much more sustainable than many other “crash diets.”  Many  studies support the practice as a valuable, reliable tool for weight loss and weight maintenance. Initially, you’ll see a marked weight loss as a result of losing water weight, but according to the author of Eat Stop Eat, each day you fast will show a loss of 0.5 pounds of true body fat.

#2  Improved tolerance of glucose

For diabetics, fasting can be a fantastic way to normalize glucose and even improve glucose variability. Anyone looking for a natural way to increase insulin sensitivity should attempt an intermittent fast.  The effects of fasting can make a huge difference in how your body processes glucose.

Generally, insulin resistance is the result of the accumulation of glucose in tissues that aren’t built for fat storage. As the body burns through stored fuel in the form of body fat, that excess accumulation becomes smaller and smaller, allowing the cells in your muscles and liver to grow increasingly responsive to insulin – great news for anyone looking to be less dependent on medications to assist these processes.

#3 Boosts your metabolism

Part of the reason intermittent fasting helps practitioners lose weight is because of the restriction of food.  When followed by regular eating, this helps stimulate your metabolism. While long-term fasting can cause a drop in your metabolism, the shorter fasts promoted by intermittent fasting have proven to increase metabolism – by up to 14 per cent, reported by one study .

This is also a more effective tool than long-term calorie restriction, which can often wreak havoc on the body’s metabolism. Weight loss often goes hand in hand with muscle loss. Since muscle tissue is what burns through calories, having less muscle leads to a drop in your body’s ability to metabolize food. Intermittent fasting, though, keeps your metabolism running smoothly by helping you maintain your muscle tissue as much as possible.

#4 Helps contribute to your longevity

Research from University of Chicago scientists revealed that intermittent fasting can “delay the development of the disorders that lead to death.”  This suggests regular practitioners can enjoy a longer, healthier life than people who eat a regular three meals a day or follow a traditional restricted-calorie diet.

A theory on this, according to the head of the National Institute on Aging’s neuroscience laboratory Mark Mattson , is that the mild stress that intermittent fasting puts on the body provides a constant threat. Thus increasing the body’s powerful cellular defenses against potential molecular damage. Intermittent fasting also stimulates the body to maintain and repair tissues and has anti-aging benefits, keeping every organ and cell functioning effectively and efficiently.

#5  Establishes a better routine

Unless you’re following a random fast type of diet, having strict eating times followed by periods of fasting can help your body develop a solid routine. You’ll be able to recognize your hunger cycles, you’ll sleep more regularly and soundly, and you’ll start scheduling appointments during convenient hours.

Of course, it can be difficult to establish this routine at first, especially if you have a family or an inflexible work schedule. However, once you’ve developed a consistent plan, you’ll soon start to see all the ways a set routine can benefit your life – and your health.

#6 Stimulates brain function

A study , discussed at a meeting of the Society for Neuroscience in 2015, revealed that intermittent fasting offers “enormous implications for brain health.” According to the study, which was undertaken on both humans and animals, stimulates the brain in several different ways: promotes the growth of neurons, aids in recovery following a stroke or other brain injury, and enhances memory performance. Not only does intermittent fasting help decrease a practitioner’s risk of developing neurodegenerative diseases like Parkinson’s or Alzheimer’s, but there is evidence to show that it may even improve both cognitive function and quality of life for people living with those conditions already.

#7  Boosts your immune system

According to scientists at the University of Southern California, fasting has the power to “ regenerate the entire immune system ” by boosting the body’s production of new white blood cells, which is how your body fights off infection. Fasting in cycles, as practitioners of intermittent fasting will do on a daily or weekly basis, enables your body to purge the damaged, old, or inefficient parts of the immune system, and replace them with newly generated immune system cells.

Studies showed that a 72 hour fast was even enough to help protect cancer patients from the harmful and toxic effects of chemotherapy treatments – which generally causes significant damage to the patient’s immune system.

Further clinical trials are needed, but many researchers are confident that intermittent fasting could be incredibly helpful for immunocompromised individuals and the elderly.

#8 Rejuvenates your skin

Acne sufferers know that one of the best ways to control bothersome skin conditions is through diet – eating only unprocessed foods and limiting consumption of dairy products. It’s no surprise, then, that regular intermittent fasting can offer impressive benefits that can be seen all over a practitioner’s glowing, radiant face. Many of these conditions are caused by food sensitivities, which can lead to inflammatory conditions and acne. After a fast, introduce foods one at a time and note any changes to your skin, to accurately pinpoint which foods should be avoided.

Intermittent fasting also has a positive effect on your hair and nails, helping them grow healthy and strong. Not only will you feel good after incorporating intermittent fasting into your lifestyle, you’ll look great, too.

#9 Reduces oxidative stress

Oxidative stress is caused by an imbalance in the body’s production of reactive oxygen and its antioxidative defenses and may lead to chronic diseases and cancers. Unstable molecules, known as free radicals, can react with important molecules like DNA and protein – damaging these molecules and creating an imbalance.

The weight reduction brought on by regular intermittent fasting can lead to a reduction in the body’s level of oxidative stress, helping prevent the development of these unpleasant conditions. A greater antioxidant capability is a huge benefit that comes with intermittent fasting and one that shouldn’t be overlooked by anyone looking to pursue improved health and well-being.

#10 Triggers Autophagy

During a fast, the body’s cells begin to undertake a process called autophagy. Over time, dysfunctional or damaged proteins can build up within cells, and this waste-removal process helps the body filter out this excess material. This process is an important part of the body’s ability to repair and detoxify, and some researchers assert that increased autophagy offers a boost in protection from many diseases, including cancer and Alzheimer’s disease.

Autophagy helps cells overcome stresses brought on by external causes like the deprivation of important nutrients, as well as internal issues like pathogens or invading infectious organisms.

You can read more about autophagy in this article here:

https://longevitylive.com/anti-aging/can-autophagy-cells-reverse-aging-and-boost-longevity/

Suggested meals

Generally, intermittent fasting means you can eat whatever healthy foods you like – within specific feeding windows, and as long as you are getting the nutrients you need. If your goal is to achieve the benefits of intermittent fasting, you won’t get there by indulging on fast food and candy. Use these meal ideas to help come up with some nutritious ways to fuel and nourish your body during your specific eating windows or periods of partial fasting.

Under 300 calorie suggestions

• one serving of oatmeal: approximately 250 calories
• roasted vegetables with balsamic vinegar and a squeeze of lemon: approximately 260 calories
• pesto salmon with kale: approximately 290 calories
• sausage with roasted ratatouille : approximately 260 calories
• prawn and squash curry : approximately 290 calories

Under 200 calorie suggestions

• light salad with spinach, feta cheese, lemon, and beetroot: approximately 150 calories
• sliced apple with 1 tbsp of nut butter: approximately 145 calories
• 100g serving of low-fat yogurt, 1sp of raw honey, 2 sliced plums: approximately 150 calories
• omelette with spinach: approximately 160 calories
• 40g of hummus and a bowl of raw vegetables: approximately 175 calories

Under 100 calorie suggestions

• one serving of miso soup: approximately 40 calories
• one soft boiled egg: approximately 70 calories
• lightly salted edamame beans: approximately 85 calories
• handful of almonds: approximately 90 calories
• one chopped and peeled kiwi: approximately 45 calories

These meals can be combined and altered to suit your taste, but it’s a good idea to try and keep each meal small and easy for your body to process. Focus on eating raw fruits and vegetables, unprocessed whole grains, organic lean protein, plenty of fibre, and lots of healthy fats to ensure that during your scheduled eating windows, you’re getting all the nutrients you need to keep your energy level up and satisfy you through your periods of partial or complete fasting.

Types of fasts

People practice fasting for a wide range of reasons, so there are several types of fasts to accommodate this variety of needs. Most will offer similar benefits, so no type of fasting is necessarily superior to others – it comes down to what works for an individual’s lifestyle, faith, or general well-being.

Dry Fasting

This type of fasting is done without food or water. A soft dry fast allows the individual to shower and brush their teeth, but an absolute dry fast, or a black fast, requires no contact with water whatsoever. This type of fasting is the most extreme and is typically practised as a spiritual act rather than for health reasons.

Liquid Fasting

While fully abstaining from solid food, a liquid fast allows individuals to consume water or juice – and has become quite trendy since the “ Master Cleanse ” or Lemonade Diet was introduced in the 1970s. This type of fast is typically short-lived, lasting between one to three days, and can include the use of laxatives and enemas to ensure full cleansing of the body’s lower digestive tract.

Partial Fasting

Also referred to as “selective fasting,” this type of fasting is incorporated into many cleanse diets or mono-diets. This means either limiting the amount of solid food consumed, or limiting consumption to specific types of food, like eating only brown rice, grapefruit, or apples.

Intermittent Fasting

This type of fasting involves sticking to a diet that cycles frequently between a period of fasting and a period of non-fasting. There are various ways to incorporate intermittent fasting into your lifestyle – alternate day fasting, one-day-per-week fasting, or 24-hour plans – but all provide similar benefits.

Planning an intermittent fast

Intermittent fasting is one of the easiest ways to see the benefits of fasting without making huge lifestyle adjustments – but it certainly takes a bit of planning. Luckily, there are tons of recommended schedules to help you figure out when to eat and when not to eat, which means that there is an intermittent fast plan that can accommodate pretty much any schedule or lifestyle.

Before embarking on a specific plan, consider what you want from the fast – are you looking to lose weight? Support a training plan? Make it a part of your regular healthy lifestyle? These factors will all play a role in helping you choose an intermittent fast schedule that will work for you.

16/8 Fast (also known as Leangains)

Fitness expert Martin Berkhan popularized this method of fasting, requiring practitioners to fast for 14 to 16 hours each day, with a restricted eating period of only eight to 10 hours – typically, you’d finish dinner at around 8 p.m. and then not eat again until noon the following day. Women sometimes have a more difficult time with longer fasts, so many women adjust this schedule to include a fast period of 14 to 15 hours, instead of the recommended 16.

For people who don’t eat breakfast, this type of fast will feel incredibly natural, but big breakfast eaters will have a harder time waiting all morning before eating their first meal. However, during your feeding window, practitioners are encouraged to fit in 2 to 3 healthy meals. Water, coffee, and other calorie-free beverages are allowed during fast periods, to help curb excessive hunger.

Possible 16/8 Fast (Leangains) Schedule

Sunday night, 8 pm: finish eating the last meal of the day

Sunday night, 11 pm: go to bed (fast time – 3 hours, so far)

Monday morning, 7 am: wake up (fast time – 11 hours, so far)

Monday morning, until noon: continue fasting, drinking only calorie-free beverages

Monday, noon: Fast time – 16 hours!

Monday afternoon, until 8 pm: enjoy one or more meals, sticking to healthy choices

Monday night, 8 pm: restart 16 hour fast

This would be considered more of a partial fast, as practitioners never truly abstain from solid foods.  The diet encourages normal eating for five days of the week, with two days of restricted calorie intake, generally between 500-600 calories per day.

Popularized by British doctor and journalist Michael Mosley, this diet allows for an easier adjustment for people who have never counted calories before – but to achieve the benefits of the fast, it’s important to eat healthy, nutritious foods both during the fast days and on regular diet days, as well.

Possible 5:2 Fast Schedule

Sunday: eat normally, choosing healthy foods

Monday: follow reduced calorie diet – throughout the day, consume only 500-600 calories

Tuesday: eat normally

Wednesday: eat normally

Thursday: reduce calories again, staying between a daily total of 500-600 calories

Friday: eat normally

Saturday: eat normally – continue to fuel your body with nutritious foods

24-hour Fast

Whether you decide to begin fasting after breakfast, lunch, or dinner, under this diet plan, you wouldn’t eat again until the same meal the next day – after 24 hours of straight fasting. This method has been quite popular for the last few years, after being touted by fitness expert Brad Pilon.

It’s important to ensure that your diet remains healthy and that you’re not overeating during your feeding periods – especially if one of your goals is to lose weight. It can be difficult to adjust to this type of fast, so experts recommend starting with 14 to 16 hours and working your way up to a full 24-hour fast. One day per week is challenging enough, and those who plan to attempt to have 24-hour fasting periods each week should take care to get enough rest and limit physical activity during the fasts.

Again, during the 24-hour fasting period, non-caloric beverages like water or coffee are permitted.

Possible 24-hour Fast Schedule

Saturday night, 8 pm: finish eating the last meal of the day

Saturday night, 11 pm: go to bed (fast time – 3 hours, so far)

Sunday morning, 7 am: wake up (fast time – 11 hours, so far)

Sunday, all day, until 8 pm: continue fasting, using non-caloric beverages to curb hunger

Sunday night, 8 pm: Fast time – 24 hours! Enjoy a healthy meal, you’ve earned it

Alternate-Day Fast

This is a rather extreme type of fast, which can be undertaken in varying degrees of intensity. Some practitioners don’t eat at all during the fasting period, while others do a partial fast with a drastically reduced intake of calories, around 500 for the day.

Since this type of fasting is difficult, it’s not recommended for beginners or people who are looking to introduce a sustainable lifestyle change. However, it has proven to be very effective in helping practitioners gain a wide range of health benefits.

Possible Alternate Day Fast Schedule

Monday: eat sparingly, sticking to a 500-600 calorie limit

Wednesday: partial fast, consume no more than 500-600 calories

Thursday: eat normally

Friday: limit intake to 500-600 calories for the day

Saturday: eat normally – focus on nutrition

Warrior Diet

After fasting or eating small amounts of raw produce throughout the day, practitioners of this type of partial fast end the day with a huge meal in the evening, within a four-hour feeding window. This style of fasting rose to notoriety in recent years thanks to fitness guru Ori Hofmekler, and was one of the first popular diets to incorporate intermittent fasting.

The Warrior Diet is based on the theory that “ancient warriors” ate lightly during the day, if at all – and feasted in the evening after bringing home their “hunt.” With this diet, your food intake will consist primarily of one evening meal, and won’t require any calorie counting.

Possible Warrior Diet Fast Schedule

Saturday night, 6 pm: finish eating last meal

Saturday night, 11 pm: go to bed

Sunday morning, 7 am: wake up

Sunday, 7 am to 5 pm: enjoy calorie-free beverages, snacks of raw fruits and vegetables

Sunday, 5 pm: enjoy a large, healthy dinner

Random Fast

This type of fasting is something we all do from time to time. Skipping a meal on occasion, when you’re not hungry enough to eat or when you’re too busy to take the time to prepare a meal and sit down to eat it. There is a misconception out there that if you don’t eat every few hours, your body will go into “ starvation mode ” and start burning muscle, but this kind of eating is fairly typical of how our ancestors lived.

Before we learned how to preserve foods for later consumption, meals were eaten whenever food was available. Following this kind of eating schedule can provide similar benefits to any other type of fasting, but is much easier to accommodate into a busy lifestyle. A Paleo-type diet is recommended when practicing a spontaneous type of fasting and can be a challenge for people who need structure and routine.

Possible Random Fast Schedule

Monday: skip breakfast, eat a healthy lunch and healthy dinner

Tuesday: reduce calorie intake to 500-600 for the day

Friday: skip breakfast and lunch before eating a large, healthy dinner

Saturday: snack throughout the day, limit to 500-600 calories

If none of these types of fasts can work with your lifestyle, don’t lose hope. Fasting doesn’t have to follow strict rules or schedules – find a fasting style that works for you. Experts recommend making one small change at a time and maintaining that adjustment for at least two weeks, to give yourself a chance to evaluate whether the change works for you or not. Then, continue to introduce further small changes as needed, until you’ve reached your ultimate goal.

Keep in mind that no matter what kind of schedule you decide to follow for your intermittent fasting, you should never go more than 36 hours without eating. When you do eat, make sure you’re eating healthy, nutritious meals – not enjoying “cheat days” by bingeing on junk food. Fasting isn’t just about not eating, it’s about helping your body function in a more effective, efficient way, and filling it with empty calories and various chemicals isn’t conducive to the process.

Can I exercise while fasting?

Since food provides your body with the fuel necessary to get through a tough workout, it is beneficial to exercise during your fast – as long as you do it correctly. Your body generally uses stored carbohydrates in the form of glycogen to power you through your workout. During a fast, when your glycogen reserves are depleted, your body will be forced to turn to other energy sources for fuel – like fat. However, experts recommend that if you’re fasting, keep your workouts short.

Photo by Mathilde Langevin on Unsplash

“When glycogen is in short supply, your body also reverts to breaking down protein – your muscles’ building blocks – for fuel,” said Kelly Pritchett , Ph.D., R.D., assistant professor in nutrition and exercise science at Central Washington University and a board-certified sports dietetics specialist.

This means that even though you will likely burn more fat if you’re exercising on an empty stomach, you could also start burning protein if you work out too hard without fueling your body with carbs – leading to a loss of muscle mass, in addition to fat.

Without food, you’ll also feel the weakening effects of lowered levels of glycogen and blood sugar. As your body adjusts to regular intermittent fasting, you’ll be able to handle this energy loss a bit better, but initially, overdoing it with your workouts could be detrimental. Make sure you’re getting enough rest to compensate for your lowered energy level before you attempt to get on the bike or start pounding the pavement.

Challenges to expect during a fast

Fasting can be a difficult practice to incorporate into a busy lifestyle, especially for individuals who have never monitored meals or counted calories in the past. For people who are newly adopting a healthy diet and exercise program, it’s a good idea to develop a routine and let your body adjust before attempting to bring in an intermittent fast plan.

Working your scheduled fast periods around your family, job, and other commitments can also be a struggle. If you have the support of your workplace and your loved ones as you incorporate fasting into your life, it will be a lot easier to stick to your eating routine. Since you will likely face a brief period of lowered energy and some mood swings initially, it can be beneficial to arrange for your first fasts to fall on weekends, or days with less scheduled activity. Be prepared to feel a bit rundown as your body adjusts to a new eating schedule.

People who have struggled with eating disorders in the past can find that fasting may trigger relapses – particularly binge eaters. The hunger that can develop during a period of fasting could lead you to overeat during your feeding days, but this is generally not a problem for people who have a healthy attitude toward food and eating.

If you’ve experienced food-related mental health issues, a diet that incorporates any period of fasting for longer than eight to 12 hours might not be appropriate.

Finally, fasting is generally not a good idea if you’re pregnant. When your body is growing another human inside it, you’ll need to fuel it frequently and make sure you’re getting all the nutrients you need in regular doses – however, there is no research to show that fasting is a harmful practice for pregnant women. Some Muslim women do choose to practice fasting during Ramadan even throughout a pregnancy, but all pregnant women are encouraged to discuss drastic dietary changes with their doctor to ensure it will be safe for the baby.

Fasting throughout history

For thousands of years, fasting has been promoted as a spiritual healing practice, employed by religions around the world. The widely recognized “ father of modern medicine ,” Hippocrates of Cos, wrote, “to eat when you are sick is to feed your illness.” Hippocrates regularly prescribed fasting as a way to speed healing from a variety of ailments.

The practice was also adopted by Greek writers and philosophers Plato, Aristotle, and Plutarch, who wrote, “instead of using medicine, better fast today.” Ancient Greeks much preferred using natural healing methods – and since humans, like animals, lose their appetite when suffering from an illness, this universal human instinct is embraced through the practice of fasting.

Even more modern thinkers have recognized the value of fasting as a way to encourage the body’s natural healing process – including Philip Paracelsus and Benjamin Franklin. However, the practice has been primarily utilized by religious groups. Virtually every religion in the world promotes fasting as for spiritual reasons, since the practice has been touted in the scriptures of Jesus Christ, Buddha, and the prophet Muhammed. Cleansing, or purification, has been embraced by a wide variety of religions and cultures throughout history.

Traditional fasting

While modern Western medicine is somewhat reluctant to accept the traditional, natural remedies of the past, the practice of fasting has managed to continue to this day. In the 1970s, the idea of “cleanse diets” emerged as a solution to help people lose weight and detoxify their bodies, and the popularity of yoga has encouraged more modern practitioners to embrace fasting as an Ayurvedic healing therapy. As more people recognize the power of the mind-body connection, the more important these self-healing practices will become – and the fact that many groups and individuals continue to fast to this day proves this ancient practice has earned a place in the modern world.

This article was first published by LongevityLive.com on the 27th of March 2017 and updated and fact-checked again on the 24th of July 2024.

About the author

Jen Miller is a former electrical engineer and product specialist with more than 20 years of product design and testing experience. She has designed more than 200 products for Fortune 500 companies, in fields ranging from home appliances to sports gear and outdoor equipment.

She founded Jen Reviews to share her knowledge and critical eye for what makes consumers tick, and adopts a strict no-BS approach to help the reader filter through the maze of products and marketing hype out there.  She writes regularly and has been featured on Forbes, Fast Company, The Muse, The Huffington Post, Tiny Buddha and MindBodyGreen.

Jess Miller

Jess Miller is a writer for popular no-BS review blog, Jen Reviews. A site that takes online generated gibberish and tells you exactly what clever life hacks and practical money-saving tips you need to know so that you can make the best decisions for you and your family. For more visit www.jenreviews.com

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TRANSFORM YOUR HEALTH

Six proven health benefits of intermittent fasting, weight loss, blood sugar, heart health, brain health, reduce cancer risk, promotes longevity.

Managing Stress and Hormonal Cycles: The Key to Successful Intermittent Fasting with Holli Abbott, Functional Nutritionist and Health Coach The Secret's of a Vibrant Woman Podcast

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Episode #11 Join Ashika and functional nutritionist Holli Abbott us they debunk common misconceptions and explore the transformative benefits of intermittent fasting. Holli simplifies the complexities of intermittent fasting, emphasizing that it goes beyond just skipping meals. Discover the critical factors to consider, including age, hormonal stages, and individual health conditions, to determine if intermittent fasting is right for you. Highlights of the Episode: 1. Intermittent Fasting Misconceptions and Benefits: Holli clarifies the true nature of intermittent fasting and its potential health benefits, including improved blood sugar balance and insulin sensitivity. 2. Managing Stress and Intermittent Fasting: Learn about the importance of managing stress and cortisol levels for optimal health and how they interplay with intermittent fasting. 3. Mindful Eating for Intermittent Fasting: Explore the significance of mindful eating, focusing on nutritious, balanced meals to maintain stable blood sugar levels and enhance overall well-being. 4. Healthy Meal and Smoothie Options: Holli shares practical meal and smoothie ideas to incorporate into your intermittent fasting routine, ensuring you get the necessary nutrients without compromising taste. 5. Intermittent Fasting and Hormonal Cycles: Understand how hormonal cycles and lifestyle factors play a crucial role in intermittent fasting, especially for women, to avoid disrupting hormonal balance. By the end of this episode, you’ll have a comprehensive understanding of intermittent fasting and practical tips to implement it safely and effectively into your lifestyle. Don’t miss out on this valuable discussion that can help you transform your health journey! If you found this episode helpful, please subscribe and leave a review. Share it with friends and family who might benefit from this insightful information.  Learn more about our guest Holli Abbott. IG:  https://www.instagram.com/holli.abbott/ LI: https://www.linkedin.com/in/holliabbott/ Facebook: https://www.facebook.com/holli.abbott Website: www.holliabbott.com Learn more about your host Ashika  ⁠https://www.ashikalessani.com/about⁠ The Secrets Of A Vibrant Woman Podcast -Apple https://podcasts.apple.com/ca/podcast/the-secrets-of-a-vibrant-woman-podcast/id1737012988 The Secrets Of A Vibrant Woman Podcast -Spotify https://open.spotify.com/show/0hKUwEQu8N2xUfdQBAXdcl?si=vDh9AfnwQjenz46x4tuPig The Secrets of a Vibrant Woman Free Facebook Private Group https://www.facebook.com/share/fhkbtxjpp7pbHnxW/?mibextid=K35XfP

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• v.185(9); 2013 Jun 11

Intermittent fasting: the science of going without

Many diet and exercise trends have origins in legitimate science, though the facts tend to get distorted by the time they achieve mainstream popularity. Benefits are exaggerated. Risks are downplayed. Science takes a back seat to marketing.

One needn’t look any further than the emerging trend of intermittent fasting for a prime example. Advocates for taking periodic breaks from eating — for up to 24 hours once or twice a week — tout it as an effective and research-backed means of losing weight and improving health. That message has been reaching more and more ears of late.

“Right now, we are at a really important juncture for fasting,” says Brad Pilon, an expert on intermittent fasting and author of the book Eat Stop Eat . “It’s becoming extremely popular.”

So popular, in fact, that it is quickly moving into fad territory, suggests Pilon. And when something becomes a fad — intensely popular but only for a short period — several problems typically ensue. For one, he says, many doctors and nutrition experts are prone to dismissing fads out of hand. So their patients and clients, while shielded from the ridiculous claims of overzealous dieting evangelists, may also lose out on the legitimate benefits of fasting done right. You know, the baby and bathwater thing.

Another concern is that promoters of intermittent fasting will, perhaps unintentionally, encourage extreme behaviour, such as bingeing. This is reflected in the photos accompanying many recent new articles on “the fast diet” or the “5:2 diet.” Often, they depict people eating heaps of high-calorie, high-fat foods, such as hamburgers, french fries and cake. The implication being that if you fast two days a week, you can devour as much junk as your gullet can swallow during the remaining five days.

There is a large body of evidence that suggests fasting can benefit both the body and brain, but most research has been conducted on animals, such as mice. Researchers studying fasting are calling for more human studies.

Not so, say more moderate proponents of fasting. Their take on intermittent fasting: eat sensibly most of the time, eat nothing for an extended period every now and then, indulge only on occasion (perhaps once a week, say, on a designated “cheat day”). There is research, they claim, to back up the health benefits of sensibly incorporating fasting into your lifestyle.

There is indeed a large body of research to support the health benefits of fasting, though most of it has been conducted on animals, not humans. Still, the results have been promising. Fasting has been shown to improve biomarkers of disease, reduce oxidative stress and preserve learning and memory functioning, according to Mark Mattson, senior investigator for the National Institute on Aging, part of the US National Institutes of Health. Mattson has investigated the health benefits of intermittent fasting on the cardiovascular system and brain in rodents, and has called for “well-controlled human studies” in people “across a range of body mass indexes” ( J Nutr Biochem 2005;16:129–37).

There are several theories about why fasting provides physiological benefits, says Mattson. “The one that we’ve studied a lot, and designed experiments to test, is the hypothesis that during the fasting period, cells are under a mild stress,” he says. “And they respond to the stress adaptively by enhancing their ability to cope with stress and, maybe, to resist disease.”

Though the word “stress” is often used in a negative sense, taxing the body and mind has benefits. Consider vigorous exercise, which stresses, in particular, muscles and the cardiovascular system. As long as you give your body time to recover, it will grow stronger. “There is considerable similarity between how cells respond to the stress of exercise and how cells respond to intermittent fasting,” says Mattson.

Mattson has contributed to several other studies on intermittent fasting and caloric restriction. In one, overweight adults with moderate asthma consumed only 20% of their normal calorie intake on alternate days ( Free Radical Bio Med 2007;42:665–74). Participants who adhered to the diet lost 8% of their initial body weight over eight weeks. They also saw a decrease in markers of oxidative stress and inflammation, and improvement of asthma-related symptoms and several quality-of-life indicators.

In another study, Mattson and colleagues explored the effects of intermittent and continuous energy restriction on weight loss and various biomarkers (for conditions including breast cancer, diabetes and cardiovascular disease) among young overweight woman ( Int J Obesity 2011;35:714–27). They found that intermittent restriction was as effective as continuous restriction for improving weight loss, insulin sensitivity and other health biomarkers.

Mattson has also researched the protective benefits of fasting to neurons. If you don’t eat for 10–16 hours, your body will go to its fat stores for energy, and fatty acids called ketones will be released into the bloodstream. This has been shown to protect memory and learning functionality, says Mattson, as well as slow disease processes in the brain.

But perhaps it isn’t so much the fasting that produces health benefits, per se, as the resulting overall reduction in calorie intake (if, that is, you don’t overeat on nonfasting days, which could create a caloric surplus instead of a deficit). That appears, at least, to be the case in slowing diseases such as cancer in mice, according to Dr. Stephen Freedland, associate professor of urology and pathology at the Duke University Medical Center in Durham, North Carolina.

“Caloric restriction, undernutrition without malnutrition, is the only experimental approach consistently shown to prolong survival in animal models,” Freedland and colleagues stated in a study on the effects of intermittent fasting on prostate cancer growth in mice ( Prostate Cancer Prostatic Dis 2010; 13:350–5). In the study, mice fasted twice a week for 24 hours, but were otherwise permitted to eat at liberty. During nonfasting days, the mice overate. Overall, they did not lose weight, counteracting whatever benefits they might have seen from fasting. Intermittent fasting with compensatory overeating “did not improve mouse survival nor did it delay prostrate tumor growth,” the study concluded.

To improve health, the goal should be to lose weight by reducing the total amount of calories consumed, suggests Freedland, rather than focusing on when those calories are consumed. “If you [don’t] eat two days a week, and limit what you eat the other five days, you will lose weight. It’s one approach to losing weight,” he says. “I’m not sure it works any better than cutting down slightly seven days a week.”

People should also be wary of books written for broad audiences that explain the science behind fasting or any other health trend, he says. One purpose of writing a book for the consumer market, after all, is to sell as many copies as possible. Authors tend to present only evidence supporting their point of view, suggests Freedland, while ignoring evidence that contradicts it. “It’s a lot of spin when you write a book.”

Editor’s note: This is a follow-up to a previous news story at cmaj.ca: “Intermittent fasting: the next big weight loss fad.”