Harry Styles has revealed the secret ingredient to his coffee – the One Direction heart-throb likes to get his caffeine kick in the form of a double espresso blended to a thick froth with a tablespoon of butter and coconut oil.
The 21-year-old singer claims that he maintains his 26in waist thanks to the coffee, which is known as bullet-proof coffee.
He recently explained to Sunday Times Style Magazine that the drink curbs his appetite: "Bullet coffee. It's black coffee with a spoonful of butter in it and a spoonful of coconut oil, all mixed up together. I've been on it for two days. You don't get hungry."
US entrepreneur Dave Asprey came up with the fatty brew after he was served tea laced with yak butter when trekking in Tibet and became intrigued that mountain climbers use the drink for energy and sustained concentration.
Butter coffee should combine organic coffee with grass-fed, unsalted butter and organic coconut oil. The result is a thick, creamy coffee with a distinctly fatty, coconut aftertaste. The double shot of caffeine is said to speed your metabolism but the addition of fat slows the digestive process, preventing a sudden energy spike, which means the coffee 'hit' is gentler and lasts longer than it normally would.
Grass-fed butter, such as Kerrygold, is also supposedly rich in cancer-fighting antioxidants, good cholesterol and vitamin K2, as well as omega-3s, fatty acids and betacarotenes, all of which are good for the brain, stamina and immune system.
However, bullet-proof coffee may be better suited to those carrying out treks in Tibet, or exerting plenty of energy on stage. One cup of butter coffee contains 400-500 calories - more than a bacon sandwich - and 50g of saturated fat, coming close to your total daily allowance of 70g in just your first drink of the day.