The bizarre ingredient Harry Styles loves in his coffee

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.

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