Many people are following the fat-friendly, ketogenic (keto) diet, where you consume 80 percent of your calories from fat and less than 50 grams of carbohydrates per day. This is considered a very low-carb diet and has a lot of restrictions on how much carbohydrates one can eat on a daily basis. But, is keto for runners practical, and if so, for what kind of runner?
Generally speaking, most runners get their energy from carbohydrates. Carbs provide our bodies with glycogen, and glycogen is our primary energy source during activity. However, when the body doesn’t have access to fuel from carbohydrates, it looks for other energy sources — like fat. The body will use fatty acids to make ketones for energy, which puts one’s body into a state called ketosis. Therefore, limiting one’s intake of carbs will force the body to burn fat for fuel.
The challenge for following a keto diet is maintaining it over time and not having “cheat” days where a person eats more carbs than allocated. The body needs time to sufficiently become fat-adapted so that it is trained to tap into fat stores for energy during activity. It can take maintaining this diet for several months before runners truly start to burn fat for fuel. Runners need to be diligent and super consistent with their food intake, and that can be a challenge for some.
For runners who run long distances, like ultrarunners, their bodies may start to tap into fat stores after 30 or 40 miles because they might have burned up their glycogen stores if they don’t refuel with carbs during the run. Burning fat for fuel can also occur for runners going long distances at lower intensities, like 15-minute miles.
The bottom line is that fat can be used for fuel under strict conditions, but runners need to be very consistent with their diet so that the body can actually tap into fat stores. However, many people may not follow the keto diet to a T, and won’t allow their body to efficiently use fat for fuel. The average person who runs at higher intensities and shorter durations should focus on carbohydrates as the main fuel source. For optimal performance, include a moderate amount carbs in one’s daily diet. But, keto for runners could make a little more sense as the length of the run or the time spent running increases substantially.