Is A Calorie Restriction Diet Right For Athletes?

Some new studies are touting the benefits of a calorie restriction (CR) diet. Can athletes benefit?

The need to shed a few pounds (or a few dozen for that matter) is hardly a foreign concept for many Americans. However, many individuals are looking for their diets to do more than just trim waistlines. They’re in the hunt for diets that guarantee longevity, reduce risk for disease and improve overall health and fitness. Subscribers to Calorie Restriction (CR) are no exception, and research suggests that this diet may deliver on some of those promises.

There are no established parameters for what constitutes a CR diet, researchers generally define it as cutting your calorie intake down to 25 to 50 percent of your body’s estimated needs. For example, an individual consuming a 2,000-calorie diet who wants to cut down by 30 percent would need to cutting calories down to about 1,400 calories per day for an extended period of time.

Studies dating all the way back to the 1930s have made a case for increased lifespan under a CR protocol, and ongoing studies on monkeys have thus far suggested decreased mortality rates. No long-term controlled studies have been conducted on humans (understandably, volunteers for such studies might be hard to come by), but population studies point toward a significant increase in health and longevity.

Personally, the very idea is enough to make my stomach growl. For many people, a few additional years may not be worth a lifetime of hunger pangs.


However, a study published in 2017 by the research team led by gerontologist Valter Longo at the University of Southern California (U.S.C.) suggests it is possible to gain anti-aging benefits without signing up for a lifetime of hunger.

Instead, a “fasting-mimicking diet,” practiced just five days a month for three months—and repeated at intervals as needed—is “safe, feasible and effective in reducing risk factors for aging and age-related diseases,” reported Richard Conniff in Scientific American last year.

Would it be worth it if CR could lead to not only a longer life, but improved athletic performance as well? Now you’re speaking my language. There are arguments for and against this for athletes.

For athletes, body composition means more than just looking good in a bathing suit or having lowered odds of chronic disease. Depending on the sport, it can be a determining factor in performance.

Triathletes and cyclists, for instance, shell out big bucks to shave a few pounds or even ounces o the weight of their bike. Ultimately, a bike can only be so light, which means it can be far less expensive and more effective to reduce our body weight instead of our gear.

For runners, weight is an even more critical factor. Carrying an extra 10 pounds of body equates to an increase of approximately 20 seconds per mile.

Those statistics don’t lie, which is why elite athletes carefully diet and exercise to achieve a “racing weight” that they feel will allow them to perform better at race time.

Look no further than Meb Keflezighi, widely known for winning the 2014 Boston Marathon and a contestant in this year’s Vermont City Marathon. Keflezighi himself has detailed the significant difference in his pre- and post-race weight, fluctuating from 121.6 pounds the day he won the Boston Marathon and was back up to 134 pounds just over one week later—normal weight for his 5 foot 5 inch frame.

This “racing weight” was achieved through restricted calorie intake combined with a fine-tuned training regimen.

While this may have been a key to Meb’s success, it should be noted his racing weight was only sustained for a short period of time as he quickly returned to his normal eating habits and body weight.


Without question, CR is an effective weight loss regimen. As athletes consume fewer calories, their bodies catabolize, or break down, tissue to make up for the energy deficit. In the initial hours of a fast, our body preferentially breaks down glycogen, the storage form of carbohydrates in our body. The amount of glycogen stored in our bodies is hardly enough to sustain us for much more than a few hours and thus our body turns to muscle and fat to supply needed energy.

The amount of fat versus muscle broken down has been the topic of numerous studies, yet no consensus has yet been reached as to whether weight lost from CR comes from fat or muscle.

This is, of course, a rather crucial distinction to make for athletes, because loss of muscle mass can not only hinder performance, but could increase injury risk.

Studies on obese subjects following a CR protocol have been promising. Participants lost weight, yet were able to maintain their muscle mass. In one such study, subjects adhered to a diet requiring a 40 percent reduction in calorie intake combined with a high protein intake and regular strength training. These subjects were able to lose a statistically significant amount of weight while preserving lean muscle mass, thus calling into question the theory that overly restricting calorie intake results in loss of muscle and therefore strength.

However, research indicates that the proportion of weight lost from muscle is higher in leaner subjects. Therefore, based on the potential loss of muscle, losing weight through CR would be most beneficial for athletes who are overweight or obese.


There are other potential downsides to CR that extend beyond muscle and fat. Just look at a nutrition facts label—it’s evident that food provides more than just calories. Adequate carbohydrates, dietary ber, protein, healthy fats, vitamins and minerals are important for our overall health and performance.

While it is true that meeting the recommendations for these nutrients can be accomplished by eating a variety of nutrient-dense whole foods, the majority of us do not.

Fitting all your nutrients in within a normal calorie diet can be di cult and becomes a challenging and even sometimes impossible task on a CR diet. Studies have found that individuals adhering to a CR diet consumed less than the Recommended Daily Allowance (RDA) for numerous vitamins and minerals. Long-term, this could lead to de ciencies that could compromise health and performance.

In the end, even if there were no downsides to a CR diet, the chances that athletes will bene t are low for one main reason: hunger. Long-term adherence to CR is extremely low, because for most people, the discomfort of being hungry ultimately trumps any health or performance benefits. In fact, the majority of studies examining CR report high dropout rates among study subjects. It seems you can’t even pay people to voluntarily go hungry for the sake of science.

As the Director of Nutrition at The Edge in Burlington, Jamie Sheahan, M.S., R.D. works closely with athletes to develop customized fueling plans to optimize their health and performance. Sheahan is also an adjunct professor of sports nutrition at UVM. An avid runner, she has completed more than 20 marathons.

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