Ketogenic diets are a popular trend for people seeking both health benefits and weight loss. A “keto diet” is high in fat and low in carbohydrates and sugar, which increases the body’s dependence on “ketones” from fat and decreases its dependence on carbohydrates. Ketogenic diets have been used medically to treat epilepsy and some types of cancer, but the concept is now becoming popular in the mainstream to be used for other purposes, including to enhance athletic performance. Diet trends are known to evolve over time, and before the keto trend, high carbohydrate diets were preferred for optimal athletic efficiency.
Researchers wanted to test the premise that keto diets are beneficial for athletic performance. They created a trial for elite athletes which compared a traditional high carb diet to a low-carb, keto style diet, to determine the metabolic benefits or drawbacks of each diet. For an average of about 20 months, the low carb athletes consumed about 82 grams of carbs and 225 grams of fat daily, versus the high carb athletes who consumed about 480 grams of carbs and 90 grams of fat daily. Both diet groups had similar training regimens and physical characteristics.
After treadmill testing, the athletes’ metabolic parameters were measured. It was found that compared to the athletes on the traditional high carb diet, the low carb keto diet group had double the rate of fat oxidation during exercise. Although previous studies have shown that short term keto dieting enhances fat oxidation, this study demonstrated a far greater effect when sticking to it for the long term. Whenever we get hungry, we begin to oxidize stored fat and carbohydrate to produce energy, but on a low carb diet the body adapts to depend more on oxidizing fat and less on oxidizing carbohydrate. Increasing fat oxidation through carbohydrate restriction is believed to have potential for reducing obesity and improve symptoms of type 2 diabetes.
Importantly, there was no difference in muscle glycogen concentrations between the two diets groups under any circumstances, including pre-exercise, during exercise, or in exercise recovery. With a low carb diet, the body can adapt to using glycogen more efficiently, and beta-oxidation powers the rebuilding of glycogen stores. This is important because even in complete starvation 30% of the brain’s energy comes from glucose. Muscle glycogen availability is an important factor in determining athletic performance, so this outcome indicates that the keto diet would likely provide enough energy for muscles, without hindering the ability to exercise efficiently. Plus, molecule for molecule, ketone bodies have deliver 25% more energy than the breakdown products of glucose. Further research is necessary, but so far, the keto diet holds promise for high level athletes.
Jeff Volek et al., “Metabolic characteristics of Keto-adapted ultra-endurance runners,” Metabolism 65, no. 3 (March 2016):100, https://doi.org/10.1016/j.metabol.2015.10.028