Ketones are naturally produced in the liver when humans are fasting, starving, consuming low carbohydrate diets or exercising for a prolonged period of time. Our bodies' muscles and brain use them for fuel when carbohydrates are lacking.
Essentially, ketones burn our stores of fat while also powering the body, a state called ketosis. This has led some athletes and nutritionists to believe that increasing ketones can not only burn fat more efficiently, but also enhance athletic performance by allowing us to continue longer with greater intensity.
"It's not a fat, it's not a protein, it's not a carb, but your body gets fuel from it," Geoff Woo, the co-founder and CEO of a San Francisco-based human-performance startup called HVMN (pronounced "human") told Business Insider.
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HVMN has developed a 2.2-ounce bottle of ketone ester called Ketone, which promises improved athletic ability and energy, as well as a heightened sense of focus. The company has developed the product through a collaboration with research done by Oxford University.
Yet, despite the promises and some positive results, many are skeptical.
"I have not yet found one ketone ester supplement that has been able to successfully put someone into the state of ketosis, no matter what dosage they take," Ben Sit, a registered dietitian and president of Evolved Sport and Nutrition, told BuzzFeed News.
Why are some experts skeptical?
Few studies have been conducted scientifically analyzing the effects of ketone supplements. While Clarke conducted a study at Oxford, using an early version HVMN's product, that gave extremely promising results, another recent study has concluded the opposite.
In Clarke's study, which was published in July 2016 in the journal "Cell Metabolism", a group of elite cyclists – including former Olympians – was divided into three groups. One group was given the ketone drink, while the other two groups were given a carb-rich drink and a fat-rich drink, respectively. They were then asked to complete a 30-minute cycling exercise, and their results were compared.
Those who drank ketone went an average of 400 meters farther than their counterparts, suggesting a clear link to enhanced performance.
But a new study, conducted by the Australian Institute of Sport with other institutions and published in October in "Frontiers and Physiology", showed precisely the converse of Clarke's research.
A group of 11 professional cyclists – who previously had competed in the Tour de France and other international events – agreed to volunteer for the Australian study. About an hour before a training session, each cyclist was given a drink that contained either ketone or a placebo. Both drinks looked and tasted essentially the same, and a second dose was given to each rider just before training began.
Each participant then used a stationary bicycle in front a screen and cycled for about 19 miles. The riders did this on two different days. On one day, they received the placebo, and on the other day, they received ketone.
Instead of seeing enhanced performance when they used ketone, the cyclists all performed worse with the supplement, the study found. On average, they went about 2 percent slower, with a 4 percent decline in power output.
Furthermore, all the riders said they felt some level of upset stomach after consuming the ketone. For one cyclist, this feeling was so severe that he was unable to begin the timed trial.
"Everyone wants simple answers," Dr. Louise Burke, the Australian study's lead author told The New York Times, pointing out that much more research needs to be done with ketone supplements to fully understand their impact on athletes. She also said other factors could have played a roll in the riders negative reaction.
HVMN's CEO thinks his experience with ketone speaks for itself
"When I drink HVMN Ketone, I feel like I'm more 'behind my eyeballs,'" Woo told BuzzFeed News. "I'm sharper, clearer. It's very similar to having fasted for multiple days, and some of the subjective focus I get from fasting, I get in a bottle."
Woo's ketone supplement retails at more than $30 per bottle.
If the results promised by Woo's product – and corroborated by Clarke's study – prove true, it may seem almost too good to be true.
People could continue to eat the fatty foods they crave by simply combining their diet with ketone supplements. This would allow them to efficiently burn through the fat, while also increasing focus and general athletic performance.
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As for now, many experts agree that the best option for most people is just to stick to a normal healthy diet.