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Keto diet may harm bone health in athletes

Endurance athletes on a low-carbohydrate, high-fat or keto diet for its alleged benefits to performance may be sacrificing their bone health.

A new Australian Catholic University study involving 28 world class racewalkers found markers of bone maintenance deteriorated after a short period on a strict keto diet.

The study, published in Frontiers in Endocrinology, indicates long-term keto diets could deplete bone mineral density and bone strength.

Study lead PhD candidate Ida Heikura, who worked with leading exercise and nutrition experts Louise Burke and John Hawley from ACU's Mary Mackillop Institute for Health Research, said the study found the keto diet disrupted bone balance by increasing breakdown and reducing rebuilding, with the effects only partially reversed when the athletes consumed carbs before and during exercise.

"Bone is continually being remodelled – being broken down and rebuilt - but we found that the keto diet disrupted this balance by increasing breakdown and reducing rebuilding,” she said.

"Long-term effects of such alterations remain unknown but may be detrimental to bone mineral density and bone strength, with major consequences to health and performance.”

The findings are sobering for advocates of keto diets who push it benefits – claiming it enables better fat burning and performance over long-distance races, she said.

Held at the Australian Institute of Sport, the study took 28 elite race walkers (23 male, five female) who were training for the 2016 Olympics or the 2017 World Championships.

Researchers put some athletes on a high-carbohydrate diet and the rest were on an energy-matched low-carb, high-fat ketogenic diet (daily carb intake of less than 50g and equivalent to a banana and a slice of bread) for three and a half weeks, after which the low carb keto group resumed carbohydrate consumption.

Diets were individually designed for each athlete by registered sports dietitians, a professional chef, and exercise physiologists. Athletes’ blood was tested for markers of bone breakdown and regeneration at rest and after exertion, both before the diet began and after they resumed eating carbs.

While exercise is generally beneficial for bone health, Ms Heikura said bone injuries represent a major challenge to consistent training and competition in high performance sport. Bone injuries can be caused by low energy availability, which is the underlying cause for an umbrella of symptoms known as RED-S (relative energy deficiency in sport), as well as inadequate vitamin D and/or calcium intake.

She said the study shows that carbohydrate availability plays a crucial role in athletes’ bone health.

"Given the injury risks and long-term outcomes underpinned by poor bone health in later life in athletes as well as individuals who undertake exercise for health benefits, additional investigations of the ketogenic diet and its role in disturbing bone metabolism are needed,” she said.