I tend to ignore health fads, but “bulletproof” (or paleo) coffee, with its intriguing mix of coffee, butter and oil, recently caught my attention. I’m not the only one – it has been sweeping the food world with a mass of chat claiming that it gives you a prolonged energy hit, sharpens your focus and keeps you feeling full.

It came about after an American health guru’s experience of drinking yak-butter tea at altitude in Tibet, and its followers range from fitness junkies across the UK to less-active urbanites looking for a mental edge. Most devotees make it at home, although it is served at the odd cafe. Fans say the caffeine combines with the fats and slowly releases its effects into the body over a long period of time. I thought I’d give it a go.

I consulted the short (but deceptively complicated) list of ingredients: coffee brewed with low-toxin beans (for general wellbeing), unsalted, grass-fed butter (grain-fed apparently doesn’t blend as well, taste as good or have as much nutritional value) and MCT oil (a manufactured oil with rumoured energising and fat-burning properties). After multiple failed health shop visits, I settled for coconut oil, which contains MCT oil in its natural, less potent form. Internet forums told me Yeo Valley butter was “mostly” grass-fed – that seemed good enough to me.

With improvised ingredients to hand, I followed the recipe, whizzing everything up “until there is a thick layer of foam on top, like a latte”. A hand blender would be “OK”, the instructions added. It’s not. After 15 minutes of furious blending, I resigned myself to the fact that my slightly bubbly liquid would have to do, and took my first sip.

The most noticeable thing was not the taste – which was like a richer, buttery (go figure!) version of milky coffee – but the texture: in particular, the thin layer of oil that coated my lips. With each gulp, the coffee got worse – the once-uniform liquid quickly separated into a dark base topped with little droplets of yellow grease, and it was accompanied by a weird and pungent smell. As for the effects: well, the coffee did keep me full, but all day I had the decidedly unpleasant feeling that there was a stick of butter stuck in my windpipe and a litre of oil sitting in my belly. I was slightly more alert than after a normal coffee, and for an extended period of time, but the discomfort more than outweighed any heightened brain power.

I didn’t feel my first attempt had given it a fair go, so, armed with a serious blender, I blitzed the next mixture to within an inch of its life. This time I was left with a not-too-unpleasant frothy brew: the smell of the coconut oil and the honey colour were appetising; and the taste, though slightly bitter and masking the flavour of the delicious coffee beans, was OK. But, with a couple of sips to go, the foam dissipated and that dreaded oily gloss began to form on top. My last mouthfuls were accompanied by the woeful feeling that I was drinking melted butter. The effects were more positive second time around – no greasy feeling in my windpipe, no sore stomach. I felt switched on. I felt good; my improved blending of the butter and oil with the coffee had made all the difference.

Next, I ventured to a couple of London cafes selling the paleo beverage to see if they were doing a better job than me. Specialty coffee shop Black Sheep Coffee serves a watered-down variation, using coconut oil and milk instead of butter: “We found [butter] masked the flavour of the coffee and was too oily,” co-owner Eirik Holth told me. The coffee – which, at £4 or £4.50 a pop, doesn’t come cheap – was undeniably delicious: smooth and creamy, with hints of cinnamon and coconut. But although I was buzzing afterwards, I think it was the effects of the higher-than-average caffeine levels in their robusta beans. My final stop was Planet Organic, one of several health food stores to embrace bulletproof (it also has pride of place on the menus of Crussh juice bars, which number more than 25 in London). This had butter, coconut oil, the lot. It tasted bitter and oily. Not a good combination. Again, I was left with a focused mind, but that only served to remind me how awful the thing had tasted.

In its full, buttery form, bulletproof is coffee as fuel and not as pleasure, so I doubt it will capture the affections of the specialty coffee industry, which prides itself on flavour above all else. Athletes or bankers needing to fire on all cylinders can gulp away, but I’ll stick with a milky flat white and a sluggish brain – the butter can stay in the fridge.