Ketogenic diets have become popular over the last decade or two, having even been adopted by some athletes. But can these diets actually improve sports and exercise performance?
Most notably, the research indicates that potential performance effects may significantly differ depending on the type of sport or exercise. However, current consensus appears to support higher-carbohydrate diets over ketogenic diets for sports performance as a whole.
The research indicates that following a ketogenic diet may improve how well athletes can oxidize (burn) fat. Since very-low-carb diets gradually lead to some metabolic adaptations, this suggests the athlete’s degree of adaptation to the diet may influence its performance.
This article provides a guide to current research on ketogenic diets for sports and exercise, the potential performance benefits and drawbacks they may have, and how keto-adaptation may influence these factors.
Table of contents
What is Keto-Adaptation?
Before we look at what the research says, let’s first define the term “keto-adaptation” and what it means.
Studies have referred to keto-adaptation as the switch in metabolic processes that allows people to extract a quick and efficient source of energy from fat.
To put this in simple terms, the idea is that it takes a certain period of time for people to adapt to a ketogenic diet. For example, if someone has been following a high-carbohydrate diet for years or even decades, then the body’s metabolic processes are optimized to burn glucose from carbohydrates for energy.
In short, the body can’t suddenly maximize the efficiency at which it can burn fat for the majority of energy.
Instead, the body must adapt to a greater focus on burning fat, rather than carbohydrates, for fuel. During this adaptation time, a continuously low carbohydrate intake slowly depletes the body’s glycogen stores, with glycogen being a storage form of carbohydrates found in the muscles and liver.
As the body’s glycogen stores reduce, and presuming carbohydrate intake remains very low, the body will begin to produce ketone bodies for energy. Ketone bodies, also known as ketones, are molecules produced from fat that provide an alternate source of energy to glucose.
What Does Research Say About Keto-Adaptation?
Now that we know what keto-adaptation means, what do studies on the subject say? And how long is this adaptation period supposed to last?
One study investigated this topic by feeding elite athletes less than 50 grams of carbohydrate per day and testing how efficiently their body burned fat:
- Time period: While previously thought to take a longer period of time, it took only 5–6 days for these athletes to burn fat for energy as effectively as athletes who had been on ketogenic diets for months.
- Fat oxidation rates: The study found that these athletes had significantly increased fat oxidation rates, meaning they burned fat for energy faster.
- Oxygen cost: Although fat oxidation improved, the athletes required 5–8% more oxygen to support this fat oxidation, which led to impaired performance levels.
Other studies have found that fat oxidation rates significantly increased on ketogenic diets within 12 weeks.
Overall, based on the available evidence, it is likely that adaptation takes days to weeks rather than several months or more.
Nutritionist’s Note: Nuances on “Adaptation” to Consider
Based on the evidence we looked at above, keto-adaptation may take from between 5–6 days to 12 weeks.
However, this specifically relates to research findings from studies on fat oxidation rates in elite athletes.
What it doesn’t consider is individual tolerance and compatibility with very low-carb diets. For example, several medical conditions (such as type 1 diabetes) can influence metabolic processes related to low-carb diets.
Additionally, it is possible for some people to struggle with a ketogenic diet and the degree of carbohydrate restriction the diet requires.
For these reasons, always remember that there’s no such thing as a one-size-fits-all diet, and ensure you discuss any significant dietary changes with your healthcare provider.
How Do Ketogenic Diets Impact Sports Performance?
There is mixed evidence on the sports performance effects of ketogenic diets, which typically restrict carbohydrate intake to less than 50 grams per day.
Let’s start with the position of the International Society for Sports Nutrition (ISSN).
In its 2024 position stand, the ISSN noted that current evidence indicates “neutral or detrimental” effects from a ketogenic diet on sports performance compared to higher-carbohydrate diets.
So, what does that current evidence look like? Several notable studies have investigated the topic of ketogenic diets for athletic performance in recent years.
Ketogenic Diets and Endurance Performance
- Athletic performance: A 2025 systematic review of six studies found mixed results on sports endurance performance from ketogenic diets. While a relatively low quality of evidence made drawing any strong conclusions difficult, some benefits, such as increased VO2 max, were observed. However, some participants described feeling a “loss of power” in the short-term and didn’t enjoy the diet.
- Aerobic performance of endurance runners: A 2024 systematic review of 12 studies reported no aerobic benefits or downsides of a ketogenic diet in endurance runners. However, it noted that some of the included studies showed participants lost body weight without losing lean muscle mass.
- Performance in athletes: A 2023 systematic review found that high-carbohydrate diets outperformed ketogenic diets for time-trial performance tests and fat-free (lean muscle) mass. In contrast, ketogenic diets led to greater total and body fat losses. Whether these weight changes could be seen as beneficial would be context-dependent in view of the athlete’s aims.
Ketogenic Diets and Aerobic Performance
- Aerobic performance in trained participants: A 2022 systematic review involving 170 participants found that ketogenic diets provided no benefits compared to other diets for VO2 max and aerobic performance. That said, they led to body weight reductions without a loss of lean mass. Overall, the evidence quality was “moderate” due to a small number of studies and significant variations in how they were designed.
- Performance in endurance runners: A 2021 systematic review analyzed data from studies looking at the impact of ketogenic diets on performance in endurance athletes, such as runners. However, no significant effects from ketogenic diets were seen.
Anaerobic Performance
- Anaerobic performance in competitive athletes: A 2026 systematic review looked at how ketogenic diets impacted anaerobic performance. While high-intensity performance, such as repeated sprints, appeared to be slightly impaired, performance was maintained in short-duration, maximal effort activities, like vertical jumps.
Strength and Power
- Carbohydrate intake and muscle growth: A 2026 systematic review found that carbohydrate intake, as a variable, had no significant effect on muscular hypertrophy (muscle growth). While the evidence quality was low and further research is required, the findings support the possibility that ketogenic diets may be compatible with muscle growth.
- Strength performance: A 2024 systematic review investigated the effects of a ketogenic diet on strength performance in trained men and women. The review found that ketogenic diets did not detrimentally impact performance, and 1-repetition max (1-RM) lift strength was maintained but not improved compared to control groups.
Terminology Explained
If you noticed any jargon in the above study summaries, then here you’ll find what it meant:
- VO2 max: This is a metric which measures the amount of oxygen someone can use during strenuous exercise. In the context of performance, a higher VO2 max means more efficient use of oxygen during sport, which is linked to stronger performance and better endurance.
- Aerobic performance: Aerobic performance refers to how well the lungs, heart, and muscles can support exercise performance over prolonged durations. For example, a soccer player needs high aerobic performance to do well in their sport. VO2 max, explained above, is a marker of aerobic performance.
- Anaerobic exercise: In contrast to aerobic performance, the short-term energy demands of anaerobic exercises are too intense to be met by the body pumping oxygen, so the body uses more immediate energy sources, such as muscle glycogen. An athlete doing a high or long jump would be a good example of this. Note: Muscle glycogen is a stored form of carbohydrate; in the case of very-low-carb ketogenic diets, the body still produces glucose from protein via a process called gluconeogenesis, which can help to maintain glycogen availability.
Keto and Performance: the Evidence in Plain English
Based on the current evidence on the ketogenic diet’s performance impacts, here are the key findings:
- Fat oxidation rates: While ketogenic diets enhance fat oxidation, this does not appear to translate into clear performance benefits compared to high-carbohydrate diets.
- Strength: Ketogenic diets don’t appear to have any positive or negative impact on strength compared to typical high-carbohydrate diets. However, this may be context-dependent and depend on protein and overall energy intake being matched. For example, if someone starts a ketogenic diet which causes overall energy intake to drop, this could lead to a decline in strength.
- High-intensity sports: Findings from studies indicate either neutral or negative impacts on sports that require high-intensity efforts, like sprinting, soccer, rugby, and tennis.
- Endurance sports: The evidence suggests ketogenic diets may have greater compatibility with endurance sports, such as marathon running, compared to their utility for higher-intensity sports. However, the evidence is mixed, and most studies note that there were no clear benefits or drawbacks associated with the diet intervention.
- Body composition: While some individual studies have found ketogenic diets may lead to muscle loss, the overall evidence supports the diet often leading to reductions in body weight while preserving lean muscle mass. This may potentially translate to sporting benefits where fat loss can improve body composition. However, a systematic review found that high-carbohydrate diets were slightly more effective for developing lean muscle mass.
Summary
As the evidence shows, most of the research on ketogenic diets for sports and exercise performance shows mixed findings.
There does not appear to be any significant evidence to support using a ketogenic diet over traditional, higher-carbohydrate diets for sports performance. However, it is equally true that many large systematic reviews find a lack of both benefits and drawbacks from a ketogenic diet as compared to high-carbohydrate diets.
Overall, though, the evidence leans toward favoring high-carbohydrate diets for sports and exercise performance, particularly for high-intensity sports.
