Many athletes are turning to untested nutritional supplements to improve physical performance. This includes a recently available and popular class of supplements known as ketone salts. However, new research from the University of British Columbia Okanagan suggests it may inhibit, rather than improve, athletic performance during high-intensity exercise, according to a recent press release.

According to Jonathan Little, assistant professor in UBC Okanagan’s School of Health and Exercise Sciences, it has previously been thought that ketone supplements improve long-duration endurance performance. The new study focused on what happens during short-duration and high-intensity workouts, like cycling up hill.

“It turns out that ketone salt supplements actually impair high-intensity exercise performance,” says Little.”

Ketone salts work by artificially elevating blood ketone levels, similar to what happens naturally during periods of starvation, and forces the body to rely on burning fat as a fuel, explains Little. Burning fat is a more effective long-term fuel, but is more complex to process and isn’t as readily accessible for quick bursts of muscle activity, as is a fuel like glucose.

“Elevated blood ketones seem to inhibit the body’s use of glycogen, the stored form of glucose, and favors burning fat instead,” says Little. “That means that the body’s quick-burning fuel cannot be accessed during high-intensity bursts of activity and athletic performance is dropping off as a result.”

In the study, Little recruited ten healthy adult males with similar athletic abilities and body mass indices. After a period of fasting, they were asked to consume either beta-hydroxybutyrate ketone salts or a flavour-matched placebo, in a randomized order, and then engage in a cycling time trial. Power output on the day participants consumed ketone salts was 7 percent lower than on the day when they consumed the placebo.

“Often these supplements are marketed as a means of improving athletic performance, but, in this case, the research tells a very different story,” says Little. “On top of that, the long-term impacts of artificially increasing blood ketone levels—essentially tricking the body into thinking it is in a state of starvation—is completely unknown.”

Both practitioners and consumers should navigate the science of supplements,  rather than relying on label marketing, says Little. While more research is needed on ketone supplements, he encourages people to proceed with caution.