Butter coffee? As disgusting as it sounds?

Can two tablespoons of butter added to your morning coffee really help you lose weight and gain a mental edge?

It sounds utterly revolting, highly improbable and an idea worthy of Homer Simpson but it hasn't stopped the butter-coffee trend taking the world of fads by storm in recent weeks. Now Irish dairy farmers are hoping to benefit from the buzz after one of its leading proponents claimed that grass-fed Irish cows produce the best butter for the concoction.

Butter coffee is the brainchild of US-based Dave Asprey who says he stumbled upon the notion of a unusually fatty highly caffeinated drink while trekking in Tibet where tea is traditionally made with yak butter.

So impressed was he by the physically and mentally agile monks he met on his Tibetan travels that he decided to emulate their diet and believes he has now found the silver bullet for overweight people.

Dubbed Bulletproof Coffee, Asprey’s caffeine cocktail uses grass-fed, unsalted Kerrygold butter and a coconut fat derivative which are blended together with an espresso shot to make a drink not unlike a fatty latte.

He says using butter made from the milk of grass-fed cows “really matters because corn or soy-fed cows don’t make butter with the same fats. Those butters don’t blend well, don’t taste good.” He claims his drink is “the creamiest, most satisfying cup of coffee you’ve ever had [AND]will keep you satisfied with level energy for six hours if you need it”.

He also says he eats 4,500 calories a day and although he has not exercised in more than two years his “world-class anti-aging physician” has put him in “the lowest percentile for diabetes risk, heart disease, and cancer, despite being a high risk for all of those when I was 10 years younger. I have lower triglyceride levels than most anyone I know.”

“We started selling it a couple of weeks ago,” said Darragh Buckley, of The Punnet Health Store and Cafe on Dublin’s Mount St. “It’s not flying out the door exactly but the people who have been ordering it absolutely swear by it.”

He said one Irish rugby international comes in three or four times a day for a shot. “It’s not my thing at all, to be honest, and I reckon people would be better off with something more natural, like maybe a shot of wheatgrass but if it is what people want, who am I to argue?”

Consultant endocrinologist and obesity specialist, Prof Donal O'Shea is more inclined to argue with the notion. "The first I heard of it was yesterday and my first thought was 'Oh Lord'," he told The Irish Times. "This is a fad that will come and go and there really is no scientific rational at all for a combination of fat and caffeine to have a positive impact on either your metabolism or your mental agility."

He accepted that western medicine does not have all the answers and “Tibetan monks have tended to live a very basic lifestyle and developed a lot of medical remedies from plants so you can’t completely ditch or disregard the things that they do but there is no scientific evidence that this drink will have any impact on anybody.”

There is, however, a large body of evidence that people who use stimulants to lose weight don’t fare all that well. “From a medical view, the history of stimulants for weight loss is unreservedly bad,” Prof O’Shea said.

But whatever about the benefits or otherwise of butter coffee, what does it taste like? Not as terrible as you might think.

The Irish Times sourced unsalted butter and coconut oil and made up a home brew and the end result was surprisingly inoffensive. Our butter coffee was greasier than a more traditional latte and coated the mouth with an oily slick but it was not unlike coffee made with cream.

Did it leave us satisfied for longer? The short answer is no. No more than two hours after we had finished the cup we were starving despite the fact that Asprey’s blog had promised us the bullet coffee would leave us full for at least six hours. And 24 hours after their one and only cup, one of the testers complained they had put on two pounds.

They blamed the coffee.