Athletes swear by ketone drinks. A new study says they don’t work.

Many competitive athletes, especially cyclists and runners, swear by ketone drinks, a popular sports supplement that promises to improve athletic performance by packing many of the purported benefits of a low-carb, high-fat, ketogenic diet into a single beverage.

You may see riders in the upcoming Tour de France quaffing ketone supplements before joining the peloton. But in a new study, the supplement didn’t amplify recreational cyclists’ racing speed and instead left them performing worse after swallowing the beverage than after a placebo. It also gave many of them gas.

“In our opinion, there is currently no evidence that acutely ingesting ketone supplements during exercise provides a benefit for an athlete,” said Chiel Poffé, a postdoctoral researcher at KU Leuven in Belgium, who has studied ketone drinks but was not part of the new study.

But the story of the rise and thud of ketone drinks, if discouraging for athletes, offers a helpful reminder to the rest of us to be wary of nutrition or fitness claims that sound a little too good to be true.

The keto diet in a bottle

It was the high expectations for ketone supplements that prompted Martin Gibala, a professor of kinesiology at McMaster University in Canada, and his graduate student Devin McCarthy, to undertake the new study, which was published online in April in the International Journal of Sport Nutrition and Exercise Metabolism.

With other collaborators, they wanted to test whether the ketone supplement would work in real-world sporting conditions.

The primary rationale for athletes to swallow ketones (which come in powdered, as well as liquid, form) was clear enough. They seemed to be getting the keto diet in a bottle.

On a ketogenic, or very low-carbohydrate, high-fat diet, the body produces ketone bodies, commonly called ketones, which can be used by the heart, brain and other organs as fuel, while the muscles start relying mostly on fat rather than carbs for energy.

Since our bodies store much more fat than carbohydrates, ketogenic diets theoretically should allow endurance athletes to train and race longer and harder before bonking or hitting the wall.

But any such effects — which have proved elusive in actual elite athletes — require weeks or months of bingeing on bacon and butter before a person’s body starts efficiently using fat as its primary fuel.

Drinking your ketones, on the other hand, seemed theoretically to promise a quick, easy way to gain the performance benefits of going keto.

Cycling slower on ketones

To see if that promise panned out, Gibala and his collaborators rounded up 23 trained, adult cyclists who regularly rode more than five hours a week.

Then they had them complete two separate 20-minute time trials on stationary bikes. Before one, they downed a ketone supplement that’s widely available commercially. On the other, they drank a beverage with similar flavoring but no ketones.

“It was a really simple study,” McCarthy said.

Some past ketone research had required hours of pre-exercise fasting or other complicated dietary routines that serious athletes wouldn’t use in training or competitions.

“We wanted to replicate a real-world scenario,” Gibala said, using a time-trial format that mimics a short, fast bike race or 5K or 10K run.

The results were unambiguous. The riders produced about 2 percent less power after drinking the ketone beverage than the placebo, which would translate into a significantly slower race time.

Their heart rates also were lower after the ketone drink, although the ride did not feel easier to them, they told the researchers.

The cyclists couldn’t and didn’t ride as hard, in other words, but the effort felt as draining as after the placebo.

Burps, bloating and bitterness

The ketone drink also had other downsides. “The taste is horrible, extremely bitter,” said Poffé, who has had occasion to sip ketone beverages as part of his research.

The flavor was so intensely unpleasant that Gibala and his colleagues had difficulty matching it in the placebo, he said.

The drink also caused stomach and intestinal problems in most of the riders, who complained of bloating, burping, flatulence, heartburn and stomach pain. Thankfully, “there were no incidences of regurgitation or projectile vomiting,” the study reports, although those have occurred in some experiments with ketone drinks.

Interestingly, these digestive side-effects have been known for some time in athletic circles but barely slowed acceptance of the supplement. “Ketone supplements are still widely used among elite athletes, to our knowledge,” Poffé said.

“I suspect some athletes would drink battery acid if someone told them it would improve performance,” Gibala said.

He and his co-authors hope their study will at least give athletes pause before supplementing with ketones before a race. “At this point,” he said, “I think it’s safe to say, it’s not likely to help.”

Poffé pointed out ketone drinks still could prove useful in other sporting contexts. Some studies, including from his group’s lab, suggest ketone supplements might aid in recovery after multiple, hard workouts or races.

They also could turn out to help during prolonged endurance events, such as a five- or six-hour-long Tour de France stage, said Brendan Egan, an exercise scientist at Dublin City University, who has studied ketone supplement use, including among 10K runners and soccer players. “Research studies have been mostly on nonelite athletes in challenges that do not mimic professional cycling,” he said.

More research is needed, though, before making recommendations about any possible, limited sporting uses of ketone supplements, the scientists agreed, and the beverages’ taste and digestive effects will probably remain an unremitting snag for many — but not all — competitors.

“They are pretty bad,” Egan said. But “if an athlete believes they work,” he said, they’ll put up with almost anything.

Do you have a fitness question? Email YourMove@washpost.com and we may answer your question in a future column.

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