Feb 4, 2015
Scheduled Interruption
Monica Van Winkle

Breaking up an eating regimen with intermittent fasts is a growing trend among athletes. Here’s a look at why it may work–and why it may not.

After waking up, a student-athlete consciously skips breakfast in the morning. He goes to class, then avoids the cafeteria at lunchtime. He doesn’t eat anything all afternoon, and as his peers dive into dinner, the athlete abstains.

He’s not sick, nor does he have an eating disorder. In fact, the next day, he’s back to snacking and eating three meals. So what’s going on with his diet? He’s taking part in an intermittent fasting program.

People have been fasting due to religious reasons for millennia. But over the past few years, intermittent fasting has gained traction in the health and fitness worlds. The scientific community has been researching its potential health implications, and, more recently, intermittent fasting has generated a buzz in athletics, where supporters credit the meal scheduling system with decreasing body fat and boosting performance.

With varied options, intermittent fasting has quickly gained a small, but growing, following. However, as with many nutritional trends, there is more to it than meets the eye. As such, it’s important that athletes learn all the facts surrounding intermittent fasting and understand its risks and drawbacks.


Intermittent fasting is true to its name–it is not a diet but rather an eating schedule that involves fasts at various intervals and for different lengths. Some plans call for 24-hour fasts, while others require skipping a single meal at random. No matter the structure, the point is to deprive the body of using food as fuel for an extended period of time.

Why would athletes want to do this? Some are looking to decrease body fat while preserving lean muscle. When the body enters a fasting state, metabolic adaptations are triggered that favor the use of fat as fuel rather than carbohydrate. For example, a 12- to 24-hour fast would decrease serum glucose and hepatic glycogen levels by 20 percent or more. This is accompanied by a shift to a metabolic mode in which non-hepatic glucose, free fatty acids, and fat-derived ketone bodies are used for energy.

Aside from burning fat, another supposed benefit of intermittent fasting is that it removes toxins. By not eating, the idea is that the body can flush out unwanted substances, leaving the athlete feeling rejuvenated.

But what may be the most significant claim about fasting for athletes is that it teaches them to manage their relationship with hunger. All intermittent fasting regimens promote the concept of “re-conceptualizing hunger” and the notion that feeling hungry is not an emergency. Participants learn that there are two types of hunger: internal and external. Internal hunger is based on physiological cues for eating, such as light-headedness or a growling stomach. External hunger is based on psychological cues, such as boredom or stress.

Intermittent fasting challenges people to sit with their hunger, rather than immediately responding to it. Athletes are supposed to step back and assess whether they are really hungry or if they need something other than food. Theoretically, when approached in this controlled manner, hunger becomes less threatening, and fasters create a reference point for interpreting true internal hunger.


There are a variety of proposed programs for intermittent fasting. The following are a handful of approaches. Total calorie needs are consumed during the feeding windows, which distinguishes intermittent fasting from calorie restriction. None of the protocols specify any time limits, so the decision to follow them periodically or permanently falls on the athletes.

The Periodic Fast: In his book, Eat Stop Eat, Brad Pilon, a former researcher in the supplement industry and current graduate student studying the metabolic effects of short-term fasting, advocates for a 24-hour fast, done two to three days a week.

Alternate Day Fasting: This plan recommends a 36-hour fast followed by a 12-hour feed. There aren’t any specific instructions for what to consume during the feed, but alternate-day fasters are encouraged to make healthy choices when fueling.

LeanGains: Followers of LeanGains complete a 16-hour fast that typically begins in the late evening and ends the following afternoon. Athletes then consume three meals during the remaining eight hours of the day.

On workout days, Mark Berkhan, the Swedish personal trainer who created LeanGains, recommends exercising immediately before the first meal in the eight-hour window and suggests eating meals containing carbohydrates, protein, and vegetables. He also encourages athletes to take 10 grams of a branched-chain amino acid (BCAA) supplement during training to prevent their muscle tissue from degrading.

Generally speaking, carbohydrate and total calorie intake are highest on training days. On rest days, Berkhan recommends increasing fat intake and decreasing carbohydrate intake. Protein and vegetables are encouraged at every meal.

The Warrior Diet: Created by Ori Hofmekler, an exercise and nutrition aficionado with an interest in survival science, the Warrior Diet is a more extreme version of LeanGains because the feeding window is reduced from eight to four hours, which allows for only one daily meal. Hofmekler suggests participants consume their daily meal immediately before exercise.

Meal Skipping: This is the most flexible option of all the intermittent fasting methods. Followers are encouraged to eat normally and skip a meal once or twice a week. The rules are flexible on what to consume, but athletes are encouraged to choose unprocessed foods.

All fasting regimens emphasize the importance of consuming nutrient-dense foods when “breaking the fast.” Meals containing lean proteins, healthy fats, complex carbohydrates, phyto-chemicals, and adequate fiber are recommended. For example, a meal of two scrambled eggs with sliced avocado, a bowl of oatmeal, and fresh berries would meet all of these needs.


If you’ve heard of intermittent fasting, you’re probably familiar with John Berardi, PhD, CSCS, cofounder of Precision Nutrition. An exercise physiologist and fitness enthusiast who refers to himself as a “professional dieter who has tried nearly every diet around to test its efficacy,” Berardi was intrigued by intermittent fasting when it was first introduced and has tried several protocols. Although previously an advocate of frequent feedings, his experience turned him into a leading supporter of intermittent fasting.

Berardi’s initial interest was sparked by a desire to lose weight to compete at the master’s level in 100-meter and 200-meter races. Already very lean at 190 pounds, he wanted to decrease his body fat and preserve his lean muscle, all while avoiding the ever-prevailing symptoms associated with calorie restriction: increased food cravings and moodiness, decreased cognition, decreased energy, hormonal dysfunction, and rebound weight gain.

Over the course of six months, he tackled six different intermittent fasting protocols. Throughout the process, he took copious notes on his cognition, energy levels, weight, body composition, and biomarkers and tracked the inconveniences of each method.

After wrapping up his intermittent fasting trial period, Berardi had dropped 20 pounds and decreased his body fat from 10 percent to four percent. He concluded the best method for him to follow going forward was a once weekly fast, lasting 20 to 24 hours. When he attempted fasting multiple days a week, he quickly experienced everything he was trying to avoid: accelerated loss of lean muscle, fatigue, and a preoccupation with high-sugar, high-fat foods when breaking the fast.

Based on his experience and results, Berardi concluded the following about intermittent fasting:

– Trial fasting is a great way to practice managing hunger.

– More frequent fasting isn’t the best way to lose body fat.

– More frequent fasting does make it easier to maintain a lower body fat percentage.

– Intermittent fasting can work, but it is not for everyone, nor does it need to be.

What can’t be deduced from Berardi’s results is the effect his physical transformation had on his athletic performance. His research only documents performance measures prior to embarking on his intermittent fasting journey.


If athletes express a desire to try intermittent fasting, it’s important that they know all the facts first. Much of the discussion on intermittent fasting centers around testimonials from those who tried it and experienced some positive results, like Berardi. To date, however, there have not been any clinical trials to prove the effectiveness of intermittent fasting protocols on improving athletic performance or decreasing body fat while increasing lean body mass. Additionally, there have not been studies that evaluate the physiological, biochemical, and psychological effects of intermittent fasting on athletes.

Beyond the research on fasting diets, it can be helpful to look more closely at the purported benefits. For instance, many athletes believe burning fat over carbohydrate during a fast leads to less body fat and maintained or increased lean mass. However, there is no scientific literature or physiological explanation for how intermittent fasting and the increased burning of fat over carbohydrate would support an improved power-to-weight ratio.

There is an abundance of literature describing how carbohydrate ingestion during exercise spares muscle tissue breakdown and delays fatigue, facilitating lean mass gains. It is also well documented that fat oxidation during exercise is not inhibited by carbohydrate consumption. Likewise, an abundance of studies have demonstrated that exercising in a fasted state encourages the loss of lean muscle mass, as muscle is also used for fuel. A close look at Berardi’s data shows that, while he may have been losing body fat, he was also losing lean body mass.

There are also flaws in the argument that fasting is an effective way for athletes to flush out toxins. In fact, the body’s main detoxification organs–the liver and intestines–need calories and fiber to do their job. Without calories, these organs lack the energy necessary to transform toxins into waste that can be eliminated. Without fiber, the removal of toxins may slow to a halt.

There may actually be some danger in following the more extreme fasting schedules, such as the Warrior Diet. Total daily energy needs should never be consumed in a four-hour feeding window.

Finally, the idea of re-conceptualizing hunger can backfire. It’s true that hunger is not an emergency, but it is a genuine signal from the brain that it’s time to eat. This message is meant to be heard. Ignoring hunger can lead to binge eating. Any athlete who struggles with interpreting hunger could benefit from working with a sports dietitian trained in intuitive eating–an evidence-based practice that targets emotional eating and helps people identify internal and external hunger without fasting.

The underlying lesson for all athletes is that the metabolic adaptations to training resemble the proposed benefits of fasting–intermittent fasting may be irrelevant to the athletic population. Exercise increases the insulin sensitivity and the ability to mobilize fat as fuel, both of which facilitate lean mass gains and fat mass losses.

If an athlete is fully informed about fasting and still thinks it’s right for them, athletic trainers, coaches, and dietitians should offer assistance. This starts with ruling out potential medical complications. For example, fasting can be particularly dangerous for an injured athlete or any athlete with a history of eating disorders, as well as female athletes with amenorrhea or oligomenorrhea. The signs and symptoms germane to eating disorders bear a striking resemblance to some of the experiences athletes undergo while fasting. Some of the warning signs that an athlete has crossed the line between experimenting with intermittent fasting and a potentially lethal eating disorder are: dramatic weight loss or gain; a preoccupation with food, calories, and weight; relentless and excessive exercise; depressive mood and mood swings; and increased criticism of their body.

If an athlete does chose to proceed with intermittent fasting, I would advise them to try it in the offseason so it doesn’t affect their performance during competitions. In addition, I encourage athletes to include sufficient fat in their pre-fast meal to delay gastric emptying and promote satiety. Adequate sleep and proper hydration are also important for the athlete to maintain baseline health. If exercising on a fasting day, I recommend working out right before the first post-fast meal to support muscle recovery.

Some intermittent fasting plans encourage the consumption of nutrients such as BCAAs and green powders. However, research has yet to substantiate their effect on energy levels, muscle synthesis and degradation, and appetite in a fasted state.

Most importantly, athletes following intermittent fasting should work with a sports dietitian who can help them meet their total energy needs, ensure the nutritional quality of meals, and monitor them for potential risks. Choosing to fast or not to fast is a personal decision. The ideal eating schedule for performance depends on the athlete. When armed with knowledge, athletic trainers and coaches can help athletes make informed decisions.

To view a list of references for this article, see below.


In a conversation with a Major League Baseball player, I asked him about his recent experiment with intermittent fasting. Here, he discusses his personal journey with the eating schedule.

What method of intermittent fasting did you follow?

I followed the LeanGains program during the offseason.

Did you see any changes in strength, power, body fat percentage, and/or speed?

I saw both pros and cons. I increased muscle while dropping body fat. My strength rose dramatically, due to the fact that I was gaining muscle and upping my bodyweight. As for speed and power, there were also some gains in those areas.

What were the cons?

I experienced headaches, mood swings, fatigue, and increased cravings early on in the program. The first two weeks were the toughest. Then, gradually it became a routine, and the consequences seemed to taper off.

Was intermittent fasting easy or difficult to follow?

It was really simple to follow because it’s not a diet–it’s a meal timing frequency. In turn, it was really flexible.

What would you tell other athletes about it?

The program showed me an alternate eating window rather than the typical breakfast, lunch, and dinner concept of meal frequency. It helped me understand what foods were good for recovery and which ones gave me energy. I wouldn’t recommend it in-season, however, due to the intense games and because I can maintain strength without it. This offseason, I’ll use the program again.


Most athletes who try intermittent fasting are looking for some sort of performance boost. However, for Muslim athletes, fasting for one month a year is an intrinsic part of their religion. During Ramadan, which is observed in the ninth month of the Islamic lunar calendar, they abstain from all food and drink from sunrise to sunset.

Staying true to the Ramadan fast while training can be difficult. Oftentimes, balancing fueling with faith requires careful planning and diligence.

In 2011, U.S. fencer Ibtihaj Muhammad partook in the Ramadan fast while training for the 2012 Summer Olympics. She adjusted by fueling and hydrating at night and was assisted by Jennifer Gibson, MSc, RD, CSSD, Sports Dietitian for the U.S. Olympic Training Center in Colorado Springs, Colo. Gibson told CNN.com that she tailored Muhammad’s diet to focus on high-protein, high-energy, and easily digestible foods, such as yogurt, bananas, peanut butter, applesauce, and rice. In addition, Muhammad would wake every 90 minutes through the night to eat and drink.

Muhammad also adapted her training schedule, moving one of her three daily practice sessions to 10 p.m., which followed her first meal of the day. And despite Muhammad’s intense training, she knew to take small breaks during her afternoon practice when she felt light-headed or dizzy.

In the NFL, Kansas City Chiefs defensive back Husain Abdullah strictly adheres to the Ramadan fast every year, even when it falls during pressure-filled summer training camps. Like Muhammad, Abdullah fuels through the night, eating one large meal at sunset, another before sunrise, and waking in between for a protein shake. On the field, the Kansas City Star reports, he wets his lips or rinses his mouth with water to temporarily relieve his thirst.

Abdullah has fasted for Ramadan since he joined the league in 2008, and during his 2010 fast–while he was with the Minnesota Vikings–coaches noticed a decline in his output. Since then, Abdullah has worked with dietitians and athletic trainers to perfect his nighttime fueling regimen so the effects of intermittent fasting are less.

-Ali Nolan


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Monica Van Winkle, MS, RD, is the owner of Nutrition in Action in Seattle, where she consults with athletes from recreational to professional levels. She is an affiliate faculty member for the Swedish Medical Center's Sports Medicine Fellowship and serves as a board member for the International Association of Eating Disorders Professionals. Previously, Van Winkle spent five years as the Sports Dietitian at the University of Washington. She can be reached at: [email protected].

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