When “energy drinks” claim to “boost your metabolism” for endurance or to “burn more fat”, there’s plenty of reason to be skeptical. When these claims aren't completely unfounded, they're usually based on tiny and cherry-picked studies. But the evidence for one drink, not yet on the market, might have more substance.

The drink is based on ketones, a class of simple molecules that includes those made by the liver out of body fat. They are part of the body’s processes for turning stored fat into energy when it has run out of carbohydrates and dietary fats.

Professor Kieran Clarke of the University of Oxford has reported in Cell Metabolism that when cyclists were given the ketone drink, they outperformed those given drinks laced with carbohydrates or fats, traveling an extra 400 meters (1,312 feet) on average during a half-hour ride.

The benefits were confirmed by measuring concentrations of sugars and acids in the athletes' muscles. "The ketone itself is inhibiting glycolysis, so that with the same exercise you're preserving glycogen and producing much less lactic acid – this hasn't been seen before," Clarke said in a statement. Since lactic acid is what causes the familiar burn that comes with pushing up to one’s limits during exercise, anything that blocks its build-up could help endurance athletes endure.

Clarke, whose research interests include the biochemistry of diabetes (where ketone monitoring is essential), was inspired to investigate ketones as a food by the Defense Advanced Research Projects Agency (DARPA), the US military’s research arm. DARPA provided funding to seek the food source that would provide soldiers with the most capacity in battle for a given weight.

The paper notes that ketosis is “often overlooked for its metabolic potential [and] poorly understood outside starvation or diabetic crisis.”

The paper reports on five studies conducted on subgroups of the 39 cyclists, some of whom were former Olympians. The first study demonstrated the different metabolic processes seen when consuming ketones before exercise and at rest, while the second compared the metabolism of cyclists drinking ketones with those getting fats or carbohydrates. Two more studies looked at the effect of ketone consumption on muscles.

It was the last study that future marketing will rely on, however. Cyclists fasted overnight and had performed a one hour moderate ride before a half-hour time trial. Each cyclist did this twice, once after being given ketones and once after an alternative energy drink, without knowing which was which. After consuming ketones, the cyclists rode 2 percent further.

Although the difference in distance cycled was statistically significant, only eight cyclists took part in the last study, although the other studies all pointed to metabolic benefits from ketone consumption.

Ketone burning requires oxygen, so the drink is only expected to benefit those engaged in aerobic exercise, excluding sprinters and others whose sport involves short bursts of activity. That still leaves a huge potential market, which Clarke hopes to tap through an Oxford spin-off company.