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Lily Canter

Keto diets and ketone supplements have gained popularity among endurance runners for their potential to delay fatigue, but new research suggests they do not give athletes an advantage.
A review of keto diet studies published in medical journal Sports Health: A Multidisciplinary Approach did not identify any significant advantages or disadvantages for endurance runners’ aerobic performance from following a ketogenic diet or having ketone supplements.
When taking part in a continuous activity such as running that increases the heart rate, our cells use oxygen to produce energy. As aerobic performance improves, the heart, lungs, and muscles work more efficiently to allow us to keep active for longer without tiring.
The review findings add weight to a warning by the International Society of Sports Nutrition that, for ultra marathon runners, following a ketogenic diet produces a range of negative symptoms. These include fatigue, headaches, poor concentration, lethargy, gastrointestinal discomfort, nausea and weight loss.

“There is no evidence that a keto diet can improve endurance performance, and plenty that it can’t. There is evidence that it is possibly bad for your bones and evidence that increasing carb intake likely improves performance,” says Andy DuBois, head coach at Mile 27 Endurance Coaching, based in Australia, commenting on the review.
He counts among his company’s clients Hong Kong ultrarunning stars Jeff Campbell and Ryan Whelan, who is now a running coach himself.
A ketogenic diet consists of at least 60 per cent fat and less than 10 per cent carbohydrates. Ketone supplements increase the amount of ketone bodies in the body, which help to break down fatty acids for fuel, a process called ketosis.
Some endurance athletes have followed a keto diet or taken supplements to shift their metabolism away from carbohydrates towards fats so, in theory, the body has enough fat stores to sustain it over long distances. When the body runs out of carbohydrates, it starts to burn fat for energy.
“In reality, most athletes end up training or racing at much higher intensities than can be fuelled by fat oxidation” – the process in which the body breaks down stored fat and uses it for energy, says Hong Kong-based nutritionist health coach Vicky Sham, a marathon and trail runner herself.












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“Following a period of a low-carb diet, the runner does not have enough muscle glycogen and isn’t fuelling with carbohydrates to support a hard workout so they can end up in a catabolic state,” Sham adds. This means their body is breaking down their muscles instead of fat, for fuel, “which is a pretty disastrous situation”.
There is limited data on the impact of a keto diet on female endurance athletes.
In the systematic review, the authors could find only 12 relevant keto studies covering 133 athletes in total, of which only one was a woman.
“If more female runners were included, I would expect even less benefits from keto diet or ketone supplements because the female hormone oestrogen can help drive fat oxidation,” says Sham. In other words, women’s bodies are already efficient at using fat as fuel.
The issue arises when runners try to mirror diets used to help the general population who are sedentary, overweight and prediabetic.
While the keto diet can help these people with managing blood glucose, insulin resistance, appetite and weight loss, the benefits do not extend to endurance performance measurements such as VO2 max, a measurement of fitness and the amount of oxygen the body can use during exercise, Sham says.

“I can imagine runners who feel bloated, overweight and have brain fog only need to read one or two [general population] study results to be convinced. They can be desperate enough to try [the] keto diet even if the scientific evidence doesn’t show improved endurance performance,” she adds.
Rather than following a ketogenic diet, healthy endurance athletes should focus on eating enough carbohydrates to fuel training, and have plenty of protein for recovery.
“Protein is superior to fat in some ways because it is nutrient dense and essential for recovery. Many runners don’t realise they do not get stronger during their runs. We only get stronger and build muscles when we rest and eat protein during our recovery. Also, fat is very hard to digest especially when you are moving your body up and down the trails,” says Sham.
Endurance athletes are more at risk of underfeeding than overeating, and adding a restricted diet on top of a high training volume can increase the risk of low energy availability, a potentially dangerous condition.
“Long distance runners who are healthy can get pretty much the same health benefits of a ketogenic diet after running for about two hours, such as fat burning. I don’t see a strong reason to bother with a ketogenic diet, when you already have the same benefits from endurance exercises,” says Sham.

DuBois agrees that a high-carbohydrate diet with sufficient protein is best for endurance runners.
He advises his athlete clients to get used to having 40 to 60 grams (1.4 to 2.1 ounces) of carbs per hour in training runs of 90 minutes or more.
“Once they are comfortable with that, they can start experimenting with different carb sources so they have options on race day. The next step is training the gut by increasing intake to 80 to 100 grams per hour and doing easy runs not long after a full meal,” he adds.
Vicky Sham’s top nutrition tips for endurance athletes

Eat plenty of carbohydrates to fuel training


Have plenty of protein for recovery


Focus on whole foods, not processed food


Eat plenty of gut-healthy fermented foods for immunity


Eat plenty of fresh vegetables and fruit as these contain antioxidants that can neutralise free radicals – unstable molecules that can damage cells

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Lifestyle

Health & Wellness

Health

Food & Drink

One of these diets ‘is possibly bad for your bones’ says an expert, while the other ‘likely improves performance’


One of these diets ‘is possibly bad for your bones’ says an expert, while the other ‘likely improves performance’.


Healthy eating

The Keto Diet

Keto or high-carb diet? For endurance running one is better than the other, data suggests

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}One of these diets ‘is possibly bad for your bones’ says an expert, while the other ‘likely improves performance’

One of these diets ‘is possibly bad for your bones’ says an expert, while the other ‘likely improves performance’