Q: Does a ketogenic diet improve athletic performance?

A. Yes — higher fat oxidation consistently improves endurance performance.

B. Yes — especially for repeated high-intensity exercise.

C. Not necessarily — fat oxidation increases, but performance benefits are not consistently demonstrated and performance may decline in some settings.

D. No — athletes cannot use fat effectively during exercise.

Correct Answer: C

The ketogenic diet has an appealing performance narrative. Restrict carbohydrate, increase reliance on fat, gain access to a much larger fuel reserve, and potentially delay fatigue during prolonged exercise.

From a metabolic perspective, part of that narrative is correct. Athletes who adapt to a ketogenic diet can substantially increase fat oxidation during exercise. What is much less certain—and much more important in performance nutrition—is whether that metabolic shift actually makes an athlete faster, stronger, or better able to complete high-quality training.

The distinction matters. Using more fat is a metabolic outcome. Performing better is a performance outcome. They are not interchangeable.

The 2024 International Society of Sports Nutrition (ISSN) Position Stand on ketogenic diets reached a fairly clear conclusion: compared with diets providing more carbohydrate, ketogenic diets have shown largely neutral or detrimental effects on athletic performance, despite producing marked increases in fat oxidation.

Why the ketogenic argument makes sense—at first

A typical ketogenic diet restricts carbohydrate sufficiently to promote nutritional ketosis, commonly around or below 50 g of carbohydrate per day. As carbohydrate availability falls, the body becomes increasingly reliant on fatty acids and ketone bodies as fuel. With adaptation, athletes can achieve remarkably high rates of fat oxidation during exercise.

For long-duration athletes, this sounds attractive. Muscle glycogen is limited, whereas body fat stores contain an enormous amount of potential energy. If an athlete could rely more heavily on fat, the argument goes, perhaps glycogen could be spared and endurance extended.

But sport is not an exercise in maximizing fat oxidation. The objective is to meet the energetic demands of the event as efficiently as possible.

At higher exercise intensities, carbohydrate becomes particularly valuable because it can support rapid ATP production and does so at a lower oxygen cost than relying heavily on fat. That distinction becomes important when an athlete is operating close to the limits of aerobic capacity, changing pace, climbing, sprinting, attacking, or repeatedly producing high power.

More fat oxidation can come with a performance cost

One of the clearest demonstrations comes from research in elite race walkers.

In a controlled study by Burke and colleagues, athletes completing intensified training followed either a high-carbohydrate diet, a periodized-carbohydrate approach, or a ketogenic low-carbohydrate, high-fat diet. The ketogenic group dramatically increased fat oxidation, reaching approximately 1.6 g/min during exercise.

Yet that metabolic adaptation came with a higher oxygen cost at race-relevant speeds. The athletes became better at burning fat, but less economical at converting oxygen into movement at the intensities that mattered for competition. The high- and periodized-carbohydrate groups improved their 10-km race performance, while the ketogenic group did not.

This was not simply an isolated finding. A later study in world-class race walkers reproduced the impairment in exercise economy and found that the ketogenic group became slower over 10,000 m despite substantially increasing fat oxidation. Restoring carbohydrate availability afterward did not reveal a delayed performance advantage from the keto-adaptation period.

That is an important performance nutrition lesson: a physiological adaptation is not automatically an ergogenic adaptation.

Training quality matters as much as the final race

Nutrition strategies should not only be judged by what happens on competition day. They also need to support the training required to get there.

In another analysis of elite race walkers, athletes consuming a ketogenic low-carbohydrate diet completed less training distance and performed interval and tempo sessions at slower speeds than athletes receiving high or periodized carbohydrate availability. During interval training, the carbohydrate-supported athletes were able to sustain higher speeds, while the ketogenic group showed higher heart rates despite moving more slowly.

For coaches and practitioners, this may be more consequential than a change in substrate oxidation measured in the laboratory. If a dietary strategy repeatedly reduces the quality of key sessions, the athlete may lose opportunities to accumulate the specific training stimulus required for competition.

Modern performance nutrition therefore increasingly focuses on matching carbohydrate availability to the demands and objectives of individual training sessions, rather than treating carbohydrate intake as something that must always be maximized—or always minimized.

What about high-intensity and team sports?

The rationale for chronic carbohydrate restriction becomes even more difficult when the sport depends heavily on glycolytic energy production.

Repeated sprinting, accelerations, changes of direction and high-intensity efforts increase the importance of carbohydrate availability. In a randomized crossover study in trained men and women, a short-term ketogenic diet reduced peak and mean power during a Wingate test and reduced distance achieved during an intermittent running test compared with a high-carbohydrate diet.

This does not mean an athlete becomes incapable of performing intense exercise after restricting carbohydrate. It means that the metabolic requirements of high-intensity sport make a chronic reduction in carbohydrate availability difficult to justify as a general performance-enhancing strategy.

That distinction is important. Being able to perform on a diet is not the same as the diet optimizing performance.

Does keto work better if athletes adapt for longer?

One common criticism of ketogenic research is that interventions may be too short to allow full keto-adaptation.

There is some validity to the question. The metabolic response to carbohydrate restriction evolves over time, and individuals differ considerably in how they respond. However, the available evidence still does not establish a consistent performance advantage after longer adaptation.

The ISSN Position Stand reviewed controlled trials across different durations and noted that only one of 16 controlled studies demonstrated a statistically significant performance benefit for the ketogenic condition. Even that study contained important interpretive limitations, including differences in energy and protein intake between groups and performance variables expressed relative to body mass.

A systematic review and meta-analysis of trained adults similarly found no convincing advantage for ketogenic diets in performance outcomes. The overall direction of evidence favored carbohydrate-rich diets for time-trial performance, while ketogenic diets were not supported as a strategy for improving high-intensity cyclic performance or maximal strength.

So longer adaptation remains a legitimate research question, but it should not be used to turn an unproven hypothesis into an established performance recommendation.

Strength, body composition and performance are different questions

The discussion becomes more nuanced in resistance-trained athletes.

According to the ISSN, ketogenic diets generally produce similar outcomes for maximal strength and strength development compared with higher-carbohydrate diets, although some studies favor the non-ketogenic condition. That is different from saying keto improves strength. The more accurate interpretation is that maximal strength can often be maintained under ketogenic conditions.

Body composition adds another layer. Ketogenic diets can produce reductions in body weight and fat mass, which may be useful in some contexts. But reductions in glycogen and its associated water can influence measured body mass and fat-free mass, while differences in energy and protein intake can make comparisons between diets difficult. The ISSN also notes the possibility of greater losses of fat-free mass under ketogenic conditions.

For a weight-category athlete, therefore, “the scale went down” and “performance improved” are two separate outcomes. A successful performance nutrition plan has to consider both.

What about ultra-endurance athletes?

Ultra-endurance sport is often presented as the strongest potential case for ketogenic nutrition because exercise intensity is lower and total duration is extremely long.

There is a reasonable physiological argument for greater fat utilization in these events, and some athletes may tolerate or prefer lower-carbohydrate approaches. Yet the evidence that ketogenic diets produce superior ultra-endurance performance remains insufficient. The ISSN position stand for single-stage ultramarathon nutrition specifically concluded that evidence supporting ketogenic diets or ketone esters for improving ultramarathon performance was lacking.

Ultra-endurance events also contain moments when carbohydrate matters: climbs, pace changes, late-race surges and efforts performed under accumulated fatigue. The fact that an event is long does not mean its physiological demands are uniformly low.

The practical question is not “carbs or fat?”

Performance nutrition rarely benefits from turning macronutrients into opposing camps.

Athletes already possess a substantial capacity to oxidize fat, and endurance training itself develops that capacity. Carbohydrate availability can then be strategically adjusted according to training intensity, competition demands, recovery time and the purpose of a particular session. Established sports nutrition guidance emphasizes carbohydrate availability when high-quality or high-intensity performance is required, while periodized approaches may deliberately reduce carbohydrate availability around selected sessions when there is a specific training rationale.

That approach is very different from maintaining nutritional ketosis every day.

For some athletes, a ketogenic diet may still be an acceptable personal dietary choice. It may also have value for body-composition goals or in specific circumstances under professional supervision. But those are different questions from whether keto should be recommended as an ergogenic strategy.

Based on the current evidence, there is no strong case for describing a ketogenic diet as generally performance enhancing.

The better question is: What fuel availability does this athlete need to perform the work required by this sport, in this session, on this day?

That is a much more useful starting point for performance nutrition than simply asking which fuel the body is burning.

Performance Nutrition Takeaway

The ketogenic diet reliably changes metabolism. It does not reliably improve athletic performance.

Greater fat oxidation may look impressive in laboratory data, but performance depends on exercise economy, power production, training quality, recovery and the ability to meet the specific energetic demands of competition.

Fuel selection is a mechanism. Performance is the outcome. Keep the two separate.

References

1. Leaf A, Rothschild JA, Sharpe TM, et al. International Society of Sports Nutrition position stand: ketogenic diets. Journal of the International Society of Sports Nutrition. 2024;21(1):2368167. doi:10.1080/15502783.2024.2368167.
2. Burke LM, Ross ML, Garvican-Lewis LA, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. The Journal of Physiology. 2017;595(9):2785-2807. doi:10.1113/JP273230.
3. Burke LM, Sharma AP, Heikura IA, et al. Crisis of confidence averted: impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible. PLoS ONE. 2020;15(6):e0234027. doi:10.1371/journal.pone.0234027.
4. McKay AKA, Ross MLR, Tee N, Sharma AP, Leckey JJ, Burke LM. Adherence to a ketogenic low-carbohydrate, high-fat diet is associated with diminished training quality in elite racewalkers. International Journal of Sports Physiology and Performance. 2023;18(7):686-694. doi:10.1123/ijspp.2022-0351.
5. Koerich ACC, Borszcz FK, Mello AT, de Lucas RD, Hansen F. Effects of the ketogenic diet on performance and body composition in athletes and trained adults: a systematic review and Bayesian multivariate multilevel meta-analysis and meta-regression. Critical Reviews in Food Science and Nutrition. 2023;63(32):11399-11424. doi:10.1080/10408398.2022.2090894.
6. Burke LM, Hawley JA, Jeukendrup A, Morton JP, Stellingwerff T, Maughan RJ. Toward a common understanding of diet-exercise strategies to manipulate fuel availability for training and competition preparation in endurance sport. International Journal of Sport Nutrition and Exercise Metabolism. 2018;28(5):451-463. doi:10.1123/ijsnem.2018-0289.
7. Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Sciences. 2011;29(Suppl 1):S17-S27. doi:10.1080/02640414.2011.585473.