Is this tiny £24 bottle the holy grail of dieting?

Its makers claim that it offers the benefits of fasting without the pain. So . . .

WheN it’s the dead of winter, it’s hard to find the motivation and energy to exercise. But clutched in my hand is a small phial of clear liquid that may help me do just that.

Described as ‘human performance fuel’, it sounds like something astronauts might slurp before undertaking a particularly onerous intergalactic task.

This magic elixir is a laboratory-made substance called ketone ester, which — so its maker claims — plunges your system into a condition known as ketosis, the metabolic state where your body is forced to burn fats instead of carbohydrates.

In the U.S., it’s the latest exercise fad, with people reporting immediate bursts of energy and clear-headedness that lead to longer, more effective workouts.

Normally, people must fast for days or follow a strict low-carb and high-fat ketogenic, or ‘keto’, diet (more about this later) to reach the point where they can exercise for longer, feel mentally sharper and potentially lose weight.

Yet one 2.2oz shot of hVMN Ketone — imagine a large vodka — could fast-track your body straight there. Developed by Oxford University scientists, the drink has been called ‘the fourth food group’.

‘It’s not a fat, it’s not a protein, it’s not a carb, but your body gets fuel from it,’ says Geoff Woo, co-founder of San Franciscobased start-up hVMN (the name is Silicon Valley-speak for human) that has licensed the new product.

Could ketone ester eventually be that modern miracle — a diet-in-a-bottle? Losing weight seems a logical result given that the drink puts the body into a state which burns stored fat.

‘We don’t have data for weight loss — the science is not quite there yet to make that assumption,’ admits Geoff. however, he adds: ‘Published, peer-review research shows Ketone suppresses appetite and we’re excited about exploring that.’

Geoff, a trim 29-year-old, says that when he drinks 120-calorie servings of Ketone, he has tons of extra energy and feels ‘more behind my eyeballs’. This seems to go above and beyond the energy drinks that merely deliver jolts of caffeine.

As one of the first British journalists to get hold of the controversial new beverage, I’m keen to see what all the fuss is about, and my expectations are high.

In preparation for the test I have been told not to have a heavy meal beforehand, and to keep a glass of water nearby.

‘Why do I need a second drink?’ I ask. Geoff grimaces. ‘You’ll probably want to wash away the taste,’ he warns.

Before I take Ketone, my blood sugar and ketone levels are tested. My blood glucose level is 172mg/dl, abnormally high as I ate two slices of almond and blueberry loaf midmorning. Oops.

My ketone ester measurement is 0.1mmol/L, which Geoff says is normal for most adults. These measurements tell me how much blood sugar, fats and fatty compounds are in my system.

I glug down the Ketone bottle. Yes, the taste is nasty — like drinking nail varnish remover. I gag and feel slightly nauseous. ‘We’re working on making it more palatable, but you do get used to it,’ Geoff reassures me.

Now, I must wait for it to work its magic — or not.

The keto diet was originally developed in the Twenties to treat children with epilepsy. Recently it has morphed into the latest weight loss fad. Sir Mick Jagger and Victoria’s Secret model Adriana Lima are among those reported to have tried it.

In a nutshell, a person’s daily nutrient intake typically works out at about 70 to 75 per cent of calories from fat, 20 to 25 per cent from protein and five to ten per cent from carbohydrates.

This means a person can eat healthy fats and oils such as butter, avocado and coconut oils, meats, seafood, non-starchy vegetables such as spinach, eggs, full-fat diary such as cheeses and heavy cream, and nuts, seeds and berries.

Only tiny amounts of carbs are allowed — say goodbye to sugar, grains, pasta, rice and potatoes. When the body is starved of carbs, its normal source of fuel, the liver converts fats into ketone molecules, sending the body into a state of ketosis. Ketone production lowers ghrelin levels, a hormone that makes you hungry. Bingo: people experience decreased appetite.

The keto diet mimics the effects of intermittent fasting, another trendy way to lose weight, feel alert and reduce inflammation.

however, many people find it hard to sustain fasting for long, and side-effects of the keto diet include lethargy, constipation and bad breath. A nasty-tasting drink seems a small price to pay for a shortcut that could give the same benefits without the effort.

Kieran Clarke, a professor of physiological biochemistry at Oxford, began researching ketones in 2001. She created ketone ester and licensed it to hVMN.

She published research in 2016 that found a group of 39 elite cyclists were able to go 400m further on a 30-minute cycling test after drinking her proprietary type of Ketone, compared with athletes who ingested carb-based or fatbased energy drinks.

however, in a more recent study, 11 athletes in Australia who were given another type of ketone-based drink performed badly and reported upset stomachs.

CLeARLY, more research is needed. But what about me? It has been 25 minutes since I chugged the super-fuel and it is time to see if it has made any difference.

I’m surprised to see immediate results. My ketone level has soared to 4.6mmol/L. ‘Wow,’ says the tech boss. ‘It would have taken me six days of fasting to get to that level. That’s very exciting.’

he’s even happier about my blood glucose measurement, which verged on diabetic levels of 172mg/dl, and has now dropped to a healthier 126mg/dl. ‘That’s an impressive 30 per cent drop,’ says Geoff. he says results like this are promising for people with type 2 diabetes.

Now I’m keen to see if Ketone will turn me into a super-athlete. For the next three hours, until the effect wears off, I put it to the test.

I speed-walk around a park, breaking into a jog for the last few laps. I’ve got tons of energy. Still feeling perky, at home I tackle a stack of paperwork I had been avoiding. My attention doesn’t wander at the first opportunity and I’m more focused. Zip. It’s done.

I haven’t eaten since my midmorning splurge of cake and have skipped lunch. Within a couple of hours my stomach is growling and I’m ready for a snack, but this may be because I’ve been so busy.

I feel the extra energy and increased cognitive effects could be a placebo response, and a single Ketone drink is certainly not enough to make any lasting difference. But I am fascinated by the results of my blood tests and feel it has had a beneficial effect.

Ketone is advertised as something you should take before a workout to get a performance boost. It’s not to be confused with raspberry ketones, already marketed for use in the UK as a fat-burning tool.

Geoff says these are chemically and physiologically different, and the results of raspberry ketones in humans are limited.

Ketone is expensive. The bottle I drank costs $33 (£24) and you can have up to three in a 24-hour period. Geoff says he hopes the drink will eventually go on sale in the UK.

The test has intrigued me enough that I would try the drink again if I had to do a challenging task, but I couldn’t afford to use it every day. And they would really have to do something about the horrid taste.