Diets play a large role in athletic achievement, as the right combination of fats, carbohydrates, and proteins can largely impact an athlete’s ability to perform. With this in mind, many athletes — especially endurance athletes — may be unknowingly compromising their ability to reach peak performance by following low-carb and high-fat diets.

Diets consisting of low carbohydrate and high fat intakes — similar to the ketogenic diet — have become commonplace due to widespread belief that they will help with weight loss, and could have further health benefits, such as normalizing blood pressure or helping with the appearance of acne. However, there are details to be considered when taking on the diet — especially as an athlete.

In a study published in Medicine & Science in Sports & Exercise in November, Jenna Gillen, an assistant professor; and Daniel Moore, an associate professor, both at the Faculty of Kinesiology & Physical Education (KPE), found that training on a low-carb diet raises the need for protein among high-level endurance athletes.

Differences between low-carb and high-fat  diets and high-carb and low-fat diets

Low-carb and high-fat diets differ greatly from their counterparts — high-carb and low-fat ones. Specifically, a high-carb and low-fat diet consists of consuming up to 65 per cent of one’s daily caloric intake from carbohydrates, and up to 35 per cent from fat. Low-carb and high-fat diets differ in that individuals on these diets consume only 25 per cent of calories from carbohydrates, and more than 60 per cent of their calorie intake comes from fat. Protein intake across the two different approaches remains steady, varying relatively little.

Low-carb and high-fat diets and their effects on athletic performance

For endurance athletes, low-carb and high-fat diets can significantly impact performance. As Gillen pointed out in an interview with U of T News, though there is more fat available for energy with low-carb diets, muscles have less carbohydrates as a fuel-source during exercise.

According to Gillen, carbohydrates are more efficient for use during exercise than fat. This is because carbohydrates are able to produce more energy per litre of consumed oxygen than fats. For this reason, low-carb and high-fat diets are less than optimal for performance, especially considering that athletes rely almost exclusively on carbohydrates for intense and high-energy expenditure activities, translating into overall lowered performance and results.

For athletes looking to manipulate their carbohydrate availability without compromising their results, Gillen suggested following a high-carb diet, and training endurance “under conditions of low-carbohydrate availability.”  Under this approach, athletes consume the optimal amount of carbohydrates required for peak performance, yet are still able to increase their energy-producing mitochondria in order to improve their endurance performance. This could, for instance, mean choosing to exercise in the morning before breakfast, which would allow your overnight fast to fuel this increase in mitochondria within muscles.

However, Gillen and Moore found in a recent study that athletes following low carbohydrate (low CHO) availability training need a larger protein intake in order to “enhance whole body protein synthesis.”

In the confines of their experiment, this increased protein requirement constituted an approximate 0.12 additional grams per kilogram per day. In reality, Gillen and Moore suggest that athletes “consume greater post-exercise protein than previously recommended (i.e., 0.4 versus 0.25 g per kg)” in order to “maximize recovery from and adaptation to low-CHO availability training.”

Recommendation for daily carb, fat, and protein intake

Moore recommended varying carbohydrate intake according to the volume of training that you plan to undertake as well as your personal body composition. For most athletes, your carbohydrate intake should vary between six and 10 grams per kilogram per day for optimum performance. Moore also emphasized that most endurance athletes meet their protein requirements as long as they are consuming a sufficient amount of calories for their training sessions.

Moore spoke on how his research has suggested that, in the case of athletes following a low-carb and high-fat diet, initial protein requirements may be elevated during the adaptation period to this diet.

While Moore continued to emphasize that this diet is not optimal for athletes wishing to reach peak performance, he recommended that those currently on the diet increase their protein intake, as “the extra amino acids that are used as energy must be replaced through the diet.”