Keto diets and ketone supplements have become popular among endurance runners hoping to delay fatigue, but new research suggests they may not provide the performance benefits some athletes expect. A review published in Sports Health: A Multidisciplinary Approach found no significant improvements in aerobic performance for runners following a ketogenic diet or using ketone supplements.
Aerobic performance in endurance sports, like running, relies on the body’s ability to efficiently use oxygen to produce energy. Improved aerobic capacity allows athletes to sustain activity longer without tiring. Despite claims that keto diets can enhance fat oxidation for energy, the review supports warnings from the International Society of Sports Nutrition, which noted potential negative effects for ultra marathon runners. Symptoms such as fatigue, headaches, nausea, and poor concentration were reported among those following a keto diet.
Andy DuBois, head coach at Mile 27 Endurance Coaching, emphasized that there is no evidence supporting improved endurance from a keto diet. Instead, he advocates for increasing carbohydrate intake, which has been shown to boost performance. Many of his clients, including top ultrarunners Jeff Campbell and Ryan Whelan, prefer high-carb diets.
A ketogenic diet typically consists of at least 60% fat and less than 10% carbohydrates, aiming to shift metabolism toward fat as a primary fuel source. However, Vicky Sham, a Hong Kong-based nutritionist and trail runner, noted that most athletes train and race at intensities requiring more muscle glycogen than fat can provide. Inadequate carb intake can lead to a catabolic state, where the body breaks down muscle for energy instead of using fat, a detrimental scenario for endurance athletes.
The review highlighted the limited data on keto’s effects on female endurance athletes, with only one woman among 133 athletes in the included studies. Sham suggested that the natural fat oxidation driven by estrogen in women may make the keto diet even less effective for female runners.
While keto may benefit sedentary, overweight, or prediabetic individuals, it does not improve key endurance performance metrics like VO2 max. Sham advises healthy runners to focus on consuming enough carbohydrates for fuel and protein for recovery. Protein supports muscle growth during rest, while fat can be difficult to digest during intense activity.
DuBois recommends a carbohydrate intake of 40 to 60 grams per hour during long training runs and increasing to 80 to 100 grams per hour as part of gut training for race day. Both experts agree that a high-carb diet combined with adequate protein intake is the best strategy for endurance athletes seeking optimal performance.
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