Can you boost running performance with ketones? We explore the research on ketogenic diets and ketone supplements. Remember, if you need more help with an injury, you're welcome to consult one of our physios online via video call.
In this article:
What are ketones?
Ketones occur naturally in our bodies and are produced by the liver and the kidneys. They help in the process of turning stored fat into energy.
When the body is starved of carbohydrates, resulting in less glycogen – the body’s first port of call when looking for a source of energy – the liver increases the production of ketones so that more energy can be produced from fat. This metabolic state is known as ketosis.
This has resulted in the rise of ketogenic diets, where people restrict their carbohydrate intake (and sometimes counter the reduction in carbohydrate calories with fat calories) to induce ketosis in an attempt to lose weight and/or perform better in endurance sports. How long it takes for ketosis to kick in depends on many factors, but consuming less than 50 grams of carbs per day for three consecutive days usually does it.
Nowadays there are also artificially produced ketone supplements to increase the ketone levels in the blood without the need to restrict one’s carbohydrate intake.
How are ketones thought to help runners?
In theory, being in a state of ketosis means that our muscles have better access to fat in their mix of energy sources, which increases the total amount of fuel that is readily available during exercise.
This would be especially handy during endurance activities, since most people have much more fat available than glycogen, and glycogen stores are typically depleted after about 90 minutes of aerobic exercise such as long-distance running.
The thinking is that if you regularly train in a state of ketosis, your body will get better at using fat as energy source and you won't “hit the wall” (that moment in an endurance race where your glycogen stores are depleted) that easily.
Endurance running on ketones – Does it improve performance?
In 2023, a team of seven scientists did a comprehensive review of the body of high-quality research that attempts to answer this question. They reviewed five studies that investigated the effect of ketogenic diets and seven studies that looked into the effect of ketone supplements, together involving a total of 132 professional and recreational endurance runners.
Each of the twelve studies used one or more of the following measures of aerobic performance: VO2max, time trials (of up to 100km!), running-time-to-exhaustion, and runners’ perceived exertion.
👉 None of the twelve studies found improved performance due to ketones.
The runners on a ketogenic diet did not do any better than the runners on a high carb, low fat diet. In one of these studies, the runners on the ketogenic diet fared worse in a time trial 4 days after having started the diet, but there was no difference in performance in subsequent time trials at 14, 28, and 42 days.
And the runners who took ketone supplements did not fare any better than those who took a placebo. In one of these studies, the runners who took a ketone supplement had a quicker time-to-exhaustion than those who took cooking oil.
The authors of the review conclude that they “did not identify any significant advantages or disadvantages of ketogenic diets or ketone supplements for the aerobic performance of endurance runners.”
They acknowledge, however, that there is further research to be done before the influence (if any) of ketones on endurance running can be described definitively. They mention the following limitations of the research they reviewed:
small sample sizes;
of the 132 endurance runners, only one is a woman – it is known that female endurance athletes rely less on carbohydrates as a fuel than males do;
the wide variety of methods that the studies used;
external factors such as temperature and humidity as well as internal factors such as differences in metabolism might have played a role;
most of the ketogenic diets lasted between three and six weeks, and it is not known how runners’ bodies might react to diets that last longer.
Ketone supplements for post-exercise recovery?
A similar review of the available research into the effect of ketones on post-exercise recovery by two scientists in Belgium in 2023 found the following.
There is evidence to suggest that ketones help to increase muscle mass after exercise and that they play a role in countering muscles getting weaker due to inactivity, e.g. when someone is injured.
There is evidence that ketones increase the body’s production of natural erythropoietin (EPO, a banned supplement in sport), which helps with improving endurance exercise performance as well as the body’s adaptation to training.
Ketone supplementation post-exercise increased the growth of capillaries (tiny blood vessels) in muscles, which improves blood and oxygen supply.
Evidence indicates that ketosis counteracts poor sleep due to hard training. (However, it doesn’t seem to improve sleep for people who don’t have sleep problems.)
Note the cautious wording, e.g. “evidence indicates”. And indeed, the authors of the review article note that the longest study thus far into the effects of ketone supplements post-exercise was three weeks, and this was for athletes who had been overtraining.
So, it is not clear whether ketone supplements have the same advantages during normal training that maintains a balance between exercise and recovery, nor do we know the long-term impact.
Is it safe to increase your ketone levels?
Ketogenic diet
Following a ketogenic diet is prescribed for some medical conditions as well as to counter obesity, and in this context its potential short- and medium-term adverse effects are quite well-researched. However, there is no reliable research on the safety of a ketogenic diet that lasts longer than two years.
Some people on a ketogenic diet suffer from “keto flu” during the first few weeks. Symptoms include nausea, vomiting, headache, fatigue, dizziness, insomnia, reduced tolerance for exercise, and constipation. Some of these symptoms can be countered by drinking enough water and getting enough electrolytes.
Longer-lasting adverse effects include:
not getting enough essential vitamins and minerals;
digestive problems such as bloating, constipation, and diarrhoea;
an increased risk of heart disease;
an increased risk of getting kidney stones;
rapid weight loss can include loss of muscle mass (not good for runners!);
potential cognitive decline due to the effect of the low-carb diet on the metabolism of the brain;
the risk of an inaccurate breathalyser reading, indicating more blood alcohol than is actually the case.
Ketone supplements
A 2020 review of the available research into whether ketone supplements enhances physical performance mentions that some participants in some of the studies reported various forms of gastrointestinal distress, including:
nausea;
diarrhoea;
flatulence;
constipation;
vomiting;
abdominal pain.
My conclusion
Currently, it is not clear whether a ketogenic diet is useful for endurance performance. From the available evidence, it seems unlikely that it will benefit you if you follow the diet for fewer than six weeks. And there is currently no evidence either which way for diets longer than six weeks.
This contradicts many endurance athletes who swear by a ketogenic diet. One explanation for this might be that some people might react differently to it than others, because our bodies and our metabolisms are not the same.
As far as side effects go, there are some worrying ones. However, we don’t actually know whether those side effects also apply to an active population, since those studies weren’t conducted on runners. Still, I would be cautious if you have a family history of heart disease or kidney stones.
👉 We definitely need more extensive research before we can draw concrete conclusions.
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About the Author
Maryke Louw is a chartered physiotherapist with more than 20 years' experience and a Master’s Degree in Sports Injury Management. Follow her on LinkedIn and ResearchGate.
