Scientists think they've discovered a fourth type of fuel for humans — beyond carbs, fat, and protein

• Ketones could supercharge the body in a way unlike any other source of fuel.
• The San Francisco-based startup HVMN recently launched a drink made of pure ketone ester that it says can help people harness its performance-boosting qualities.
• The company partnered with Oxford University to leverage $60 million worth of scientific research with elite athletes.

The nutrition label on a shot-size bottle of this clear, odorless liquid defies traditional explanation. It contains 120 calories — roughly the equivalent of a hearty slice of bread — yet it has no fat, no protein, and no carbohydrates.

Those calories instead come from ketones, an ingredient that Geoff Woo, the cofounder and CEO of a San Francisco-based human-performance startup called HVMN (pronounced "human"), likes to call "the fourth macronutrient."

"It's not a fat, it's not a protein, it's not a carb, but your body gets fuel from it," Woo told Business Insider.

With that in mind, Woo launched his company's first ketone product, a 2.2-ounce bottle of ketone ester called Ketone. The drink, now available for preorder, promises improved athletic ability and energy, and a heightened sense of focus.

To make the product, HVMN leveraged more than a decade and $60 million worth of scientific research through an exclusive partnership with Oxford University.

Ketone could boost performance 'unlike anything we've ever seen'

Most of the food we eat contains carbs. The carbs in fruit come from naturally occurring sugars; those in potatoes, veggies, and pasta come from starch. They're all ultimately broken down into sugar, or glucose, for energy.

When robbed of carbs, the body turns to fat for fuel.

In the process of digging into its fat stores, the body releases molecules called ketones. A high-fat, low-carb diet (also known as a ketogenic diet) is a shortcut to the same goal.

Instead of going without food, someone on the keto diet tricks the body into believing it is starving by snatching away carbohydrates, its primary source of fuel.

This is why as long as you're not eating carbs, you can ramp up your intake of fatty foods like butter, steak, and cheese and still lose weight. The body becomes a fat-melting machine, churning out ketones to keep running.

If you could ingest those ketones directly, rather than starving yourself or turning to a keto diet, you could essentially get a superpower.

Brianna Stubbs, a postgraduate student at the University of Oxford who leads research at HVMN, put it this way: "You could run up a wall, but you don't want to."

Studies with athletes have found that combining ketones and carbs produces what Stubbs called a "stacking effect."

That performance boost is "unlike anything we've ever seen before," said Kieran Clarke, a professor of physiological biochemistry at Oxford who's leading the charge to translate her work on ketones and human performance into HVMN's Ketone.

This is an energy drink that goes far beyond caffeine

In a small study published in July 2016 in the journal Cell Metabolism, Clarke gave an early version of HVMN's ketone drink to a group of elite cyclists (some of whom were former Olympians) and compared how they performed on a 30-minute cycling exercise with one group given a carb-rich drink and one given a fat-rich drink.

The high-performing cyclists on the ketone drink went an average of 400 meters farther than the best performers who'd had the carb or fat drinks. They most likely didn't even feel a difference, Clarke said.

"It's not like caffeine or anything — it's not a stimulant," Clarke said. "If you're not watching what you're doing, you think, 'Oh, I'm doing all right, everything feels normal,' but then you look down, and all of a sudden you see, 'Oh, wow, I've gone a lot further than usual!' You'll find on a rowing machine, for example, you're going a lot faster, and you didn't even realize it."

A bottle of HVMN's Ketone delivers 25 grams of beta-hydroxybutyrate, one of the substances the body produces during a fast or a period of starvation.

Within an hour of consuming the drink, you can raise your ketone levels to a level similar to what you would see after at least seven days of fasting, Woo said. That's based on two small studies published in the journal Frontiers in Physiology in which adults were given drinks containing either ketone ester or ketone salts, a supplement that combines ketones and sodium.

When we (Erin Brodwin, a science correspondent, and Melia Robinson, an innovation reporter) tried Ketone for ourselves in October, we measured our blood glucose and ketone levels before and after drinking it. To our surprise, we saw immediate and measurable results.

Erin's ketone level rose to 4.2 millimoles per liter from 1.2. Melia's ketone level rose to 6.0 mmol/L, a deep state of ketosis that can typically be achieved only through fasting, from 0.6.

Most people's ketone levels are around 0.1 mmol/L, but we started with higher levels because one of us happened to be trying a fast, while the other was eating a low-carb diet.

But did those increases reflect a difference in performance? It's hard to say.

Two people do not make for a sufficient sample size in a study of the drink's effects, and it's impossible to separate our perception from any placebo effect. Still, both of us noticed some improvement in focus, and we both skipped our usual 3 p.m. coffee — a change we didn't notice until hours later.

Ketone "sort of like makes life easy," Clarke said. "Rather than making you feel as though your heart is racing or you're exhausted ... you have this energy — energy you just don't normally have."

Read more:

• This chart is easy to interpret: It says we're screwed
• How Uber became the world's most valuable startup
• These 4 things could trigger the next crisis in Europe

Read the original article on Business Insider UK. © 2016. Follow Business Insider UK on Twitter.