Sports researchers say ketogenic diets don’t boost performance

A position paper from a prominent sports nutrition research group has concluded ketogenic diets are generally not helpful for achieving the best performance, though such diets might have other benefits.

The International Society of Sports Nutrition (ISSN) published a position paper on ketogenic diets in its captive journal yesterday. Listed as authors were many of the most prominent members of the organization who comprise a who’s who of sports nutrition research in North America.

The paper summarizes what recent research has to say about ketogenic diets as they relate to sports nutrition. It includes 149 citations.

Ketogenic diets are generally low in carbohydrates and high in fats. The goal of such diets is to induce ketosis, or the process by which the body burns stored fat instead of glucose for energy.

Most people adopt a ketogenic diet to lose weight, and these diets appear to achieve this by inducing satiety and consequently restricting caloric intake. Health authorities have noted, however, that many people find the most restrictive of these diets to be very difficult to follow for an extended period.

Secondary reasons for following a keto diet include a perception that it could be healthier for many reasons. Some promoters claim, for example, that humans were not “made” to digest large quantities of carbohydrates and that our progenitors ate mostly meat proteins and fats combined with crude, low-carbohydrate plantstuffs.

What is ketosis?

During ketogenesis, the body produces three kinds of ketone bodies in the liver: acetoacetate, beta-hydroxybutyrate (βHB) and acetone (ketones). These compounds, being water soluble, can easily disperse throughout the body to provide an alternative form of energy for the body’s cells.

Ketosis generally occurs when the body’s glucose stores are low, such as during fasting. It can also occur when ready stores of glucose and glycogen have been depleted during long-duration aerobic exercise.

The ISSN authors noted that interest in keto diets to boost endurance exercise outcomes began in the 1980s. Interest was further aroused by a 2015 paper that postulated “keto adapted” athletes — those who had trained their bodies to preferentially use ketone bodies as fuel — could have an advantage in endurance events.

At the time, many athletes were experimenting with the diets, the ISSN authors said, but there was little clinical data to substantiate whatever effects they claimed to be experiencing.

Ketogenic diets do appear to help users lose weight, the authors noted, but it seems to come at the expense of lean body mass. In other words, people lose weight, but they lose muscle tissue, too.

Including the 2015 paper, the ISSN authors evaluated 16 studies done on human athletes. They cited a significant lack of data pertaining to female athletes.

ISSN position points

After evaluating the data contained in those studies, the authors came to the following conclusions that athletes and trainers should consider when thinking about whether to adopt a ketogenic diet:

Kleiner: Paper helps summarize what is known, and what still needs to be elucidated

Susan Kleiner, Ph.D., a clinical nutritionist and founding member of the ISSN, was not involved with the ketogenic position paper effort. But she said it will help direct future research to fill in gaps in the field.

“The paper walks the reader through the basics of energy metabolism and the process (of both diet and metabolism) of achieving ketogenesis,” she said. “Along with reviewing the current body of evidence, it is a guide to missing data that could generate new studies, as well as what methods are required to deliver reliable and reproducible data of the quality to be included in a position stand review.”

Kleiner said she has three key questions regarding the ketogenic diet, and the position paper addresses some of these issues. While 16 papers are not a lot of data to draw upon, there are good answers for the first two of her questions below, and less data pertaining to the third.

She asks:

1. How does a keto diet affect both endurance and strength training performance?

2. How does a keto diet affect body composition and body weight?

3. Do we know the difference in effects of the keto diet on males versus females?

Conclusion: Using a keto diet not a winning strategy

The ISSN authors concluded by saying the evidence argues against using a ketogenic diet for an active athlete.

“The research to date indicates that a ketogenic diet has largely neutral or detrimental effects on athletic performance,” they wrote. “For endurance events, a ketogenic diet interferes with the body’s ability to generate energy from glucose, a necessity when performing at high intensities observed in real-world competitions. Even when one is ‘keto-adapted,’ performance under real-world race conditions is impaired in endurance athletes. Special consideration is needed for female athletes, as sex differences in metabolic pathways, mitochondrial function, and the effects of ovarian hormones may nullify many desirable adaptations from ketogenic diets that are observed in male participants.”

However, if the goal is simple weight loss, the keto diet might make sense. But even here, it’s problematic for athletes, who are seeking to maintain or increase muscle mass while shedding pounds of fat.

“For body composition, ketogenic diets appear to be superior to higher carbohydrate diets for reducing body weight and fat mass, but they are suboptimal for increasing fat-free mass,” the authors concluded.