Keto and Athletic Performance: 2025 Systematic Review Summary
A systematic review published in a peer-reviewed journal in 2025 examined the effects of ketogenic diets on athletic performance across multiple sports and training modalities. Drawing on six clinical trials covering 98 subjects in cycling, ultra-running, triathlon, and strength sports, the review measured VO2max, time-trial performance, fat oxidation, body composition, and muscle damage markers. The headline finding: keto shows a trend toward higher fat oxidation and reduced carbohydrate dependence, but this metabolic shift does not consistently translate into improved race times or peak-output performance, particularly for elite athletes. For ultra-endurance competitors, the fuel switch can be a genuine advantage; for sprint and power-based disciplines, strategic carbohydrate availability still wins.
What the 2025 systematic review examined
The systematic review, published in PMC ([PMC12237284](https://pmc.ncbi.nlm.nih.gov/articles/PMC12237284/)), analysed randomised controlled trials and high-quality observational studies on ketogenic diets in competitive and recreational athletes. Researchers included studies on cyclists, ultra-runners, triathletes, and strength-sport athletes. The review assessed outcomes including maximal oxygen uptake (VO2max), time-trial performance, fat oxidation rates, body composition, and markers of muscle damage. The editorial published in Frontiers in Nutrition ([PMC12888864](https://pmc.ncbi.nlm.nih.gov/articles/PMC12888864/)) integrated these findings with existing knowledge on exercise physiology and chronic conditions. The overall evidence base is limited: the review analysed six clinical trials encompassing 98 subjects in total.
Where keto consistently helps: fat oxidation
Athletes on ketogenic diets showed a trend toward higher fat oxidation rates at submaximal intensities, though the differences were not statistically significant. Long-duration ultra-endurance athletes on keto were able to sustain stable energy output with reduced dependence on carbohydrate stores, which can be an advantage in events lasting many hours where glycogen depletion is a limiting factor. Some ultra-distance competitors reported reduced gastrointestinal distress compared to high-carbohydrate strategies. Ketosis appeared to preserve muscle glycogen use, allowing athletes to go further before hitting the wall.
Where keto falls short: high-intensity and peak-output events
For high-intensity sport and competition-level performance, the review found less compelling evidence in favour of keto. VO2max and strength-output metrics showed no statistically significant differences between keto and control groups. Most studies included in the 2025 review showed no consistent improvements in performance on keto. Reviewers concluded that for events with significant anaerobic demands, strategic carbohydrate availability remains superior.
Keto and body composition in athletes
The review noted that keto tends to reduce body weight and fat mass in athletes, which may benefit performance in weight-sensitive sports such as climbing, gymnastics, or combat sports. However, some studies found that lean mass preservation was challenging without adequate protein intake, and that the body composition benefits were often similar to those achieved with calorie-controlled mixed diets of equal protein content. For strength athletes, there was no consistent benefit in maximal strength or power output from ketogenic diets compared to higher-carbohydrate protocols.
How athletes can apply these findings
The 2025 review and accompanying editorial suggest that keto is best used as a specific tool within a periodised nutrition plan, not as a permanent dietary identity. Practitioners recommend using dedicated keto training blocks to enhance fat adaptation, then strategically reintroducing carbohydrates before competition or high-intensity training phases. This approach, sometimes called carbohydrate periodisation, attempts to capture the fat-oxidation benefits of keto while preserving the capacity for high-intensity performance. Athletes should work with a sports dietitian to tailor the protocol, as individual responses to keto vary significantly.
FAQ
Is the keto diet good for endurance athletes?
For ultra-endurance athletes competing in events lasting many hours, keto can improve fat oxidation and reduce dependence on carbohydrate stores. However, for events with significant high-intensity phases such as marathons or triathlons, keto has not shown consistent performance benefits over carbohydrate-inclusive strategies, according to the 2025 systematic review.
Does keto help or hurt muscle gain?
The evidence is mixed. Keto does not consistently support muscle gain as well as higher-carbohydrate, higher-protein diets for strength athletes. Lean mass can be preserved on keto with adequate protein intake, but most studies show no advantage for hypertrophy or maximal strength compared to standard sports nutrition protocols.
Can an elite athlete perform on a ketogenic diet?
Some elite athletes use keto successfully, particularly in ultra-endurance disciplines. However, the 2025 systematic review found no consistent performance gains for high-intensity events. Most elite performance coaches continue to recommend carbohydrate-inclusive strategies for peak competition performance, while acknowledging that keto has a role in targeted training periods.