Three-and-a-half weeks later the groups were tested for bone markers after fasting, eating, exercising and again after a carbohydrate “restoration” feed.
The athletes on the keto diet displayed an increase in the markers of bone breakdown and a reduction in the markers of bone formation.
This is strong circumstantial evidence that the ketogenic diet could have adverse effects on bone health in elite athletes.
Professor Amanda Salis
The researchers, whose work was published in Frontiers in Endocrinology, believe this may be the result of an inflammation response.
Louise Burke, the head of sports nutrition at AIS, said when there was low carb availability during exericse, there were “increases in the inflammatory response to exercise and there’s a number of … activities that are the result of that, one of them being the bone-change”.
“You would predict that if this was the daily environment in which they were getting more bone breakdown then, over time, that would lead to bone loss or loss of bone mineral density,” she said.
Professor Amanda Salis, from the University of Western Australia’s School of Human Sciences, says the study (which she was not involved with) showed that “elite athletes who underwent the ketogenic diet were breaking down more bone and rebuilding less bone than the elite athletes who underwent the non-ketogenic diet”.
“This is strong circumstantial evidence that the ketogenic diet could have adverse effects on bone health in elite athletes. It is not clear if these same results would also apply to people who are not elite athletes.”
While the ketogenic diet may remain popular in certain circles, it is no longer popular among the elite athletes Burke works with at the AIS.
Their research has found that for athletes needing to work at a high intensity (80-85 per cent of VO2 max) “it is not beneficial”.
This is because fat requires more oxygen to burn than carbohydrates, Burke explains. So when an athlete needs to find another gear so they can sprint to the finish line, or power up a hill or break away from the pack, they have to use more oxygen or slow down.
“In our studies, we found it might be an OK thing to do in very moderate ultra-endurance exercise but when we’re dealing with higher intensity elite athletes, it’s actually a disadvantage,” she said.
For this reason, when Burke now tries to recruit athletes to try the keto diet so they can further explore the “bone angle”, they decline.
Burke insists no nutrition study is “black and white”. “There’s always context,” she said, advising people to “weigh up the evidence and see where it points”.
For long-term bone health and high-performance sport however, the evidence does not point to the ketogenic diet.
Sarah Berry is a lifestyle and health writer at The Sydney Morning Herald and The Age.