What should you eat if you want to run an ultramarathon or bike in the Tour de France?

Conventional wisdom says to load up on carbohydrates, which the body turns into glucose and, ultimately, energy.

But a team of biochemists from the University of Oxford have announced a different strategy.

They say add some ketones to your diet and you might be able to pull ahead of your competitors, if only by a nose.

Like glucose and fat, ketones are an energy source for the body. But they can’t be obtained from food.

Instead, the body produces ketones by breaking down fat — something that happens when there isn’t enough glucose coming in from a person’s diet, or in the case of diabetes, if the body can’t produce or use insulin to break down that glucose.

Those on the ketogenic diet induce this state of “ketosis” on purpose by eating few carbs and lots of fats.

Read more: The keto diet is gaining popularity, but is it safe? »

Ketones in the lab

The Oxford scientists say they have found a way to bypass these dietary acrobatics by creating an edible — if not palatable — ketone food in the lab.

The food, which the scientists named ∆G®, is liquid at room temperature and tastes “pretty horrid,” according to the study’s first author, Dr. Pete J. Cox, a clinician at the university.

He and his colleagues tested it as a source of energy on a group of endurance bicyclists, including some former Olympians.

They gave the cyclists energy drinks — some with ketones, some with carbs, some with fats, and some mixed — and asked them to cycle at high intensity for up to two hours.

The cyclists who got the ketones were able to cover about 400 more meters than those given the other fuels.

They also had less lactate, a byproduct of glucose breakdown, in their blood. Lactate is thought to be associated with muscle fatigue, so researchers think this might help explain their better performance.

That 400-meter gain might seem modest, but it is of interest in a world where the Tour de France is won by a difference of just four minutes. The World Anti-Doping Agency told Cycling Weekly last year that ketones are considered a legal supplement.

A high-energy, low-volume drink might also be a useful part of a combat soldier’s kit.

In fact, much of the group’s funding came from Defense Advanced Research Projects Agency, the research arm of the U.S. Army.

Read more: Can a ketogenic diet help treat bipolar disorder? »

The good and the bad

The drink is set to be produced commercially within about a year.

Kieran Clarke, Ph.D., a study co-author and a physiological biochemistry professor at the University of Oxford, told Healthline that once the manufacturing process is scaled up, the drink will cost about $1.32.

The performance boost the authors report agrees with many of the claims made by proponents of the ketogenic diet. Besides keeping weight down, dieters say being in a state of ketosis improves their mood, focus, and energy.

Those critical of the diet say that eating such large amounts of fat puts dieters at risk for heart conditions later on, as well as robbing them of essential nutrients and fiber.

It’s “too much of the bad stuff and not enough of the good stuff,” says registered dietitian Katie Ferraro, who is also an assistant clinic professor of nutrition at the University of California, San Francisco, Graduate School of Nursing.

It’s difficult to stay on a truly ketogenic diet, Ferraro told Healthline. Most people cheat. And if they don’t, they often develop terrible headaches and constipation.

Still, she thinks the researchers’ findings are interesting and valid, if not applicable to the everyday person.

“If you’re competing for a short time at a high intensity level, then maybe that’s worth it,” said Ferraro.

Clarke agrees that ketone fuel, whatever its source, isn’t for everyone.

“There’s no doubt that the Atkins diet works, but for people who are normal weight and relatively sedentary and don’t compete in large marathons, then I can’t see any benefit whatsoever,” she told Healthline.

In fact, the ketone drink would not even benefit all athletes. Sprinters, for example, wouldn’t see a performance boost because that kind of exercise is anaerobic. Ketones need oxygen to be of use.

For most people, she said, issues with weight can be solved simply by eating less rather than following a strict, challenging diet.

Clarke is more excited about the potential benefits of ketones to treat diseases like Parkinson’s, type 2 diabetes, and epilepsy.

But for healthy people whose jobs don’t require testing the limits of physical endurance, ∆G® is not for you, she said.

“I certainly am not drinking it,” Clarke said.

Keep reading: Is there such a thing as a healthy energy drink? »