Harry Styles has been known to be very conscious and strict when it comes to his diet and exercise regimen. It turns out the One Direction heartthrob has a secret diet that he religiously follows to maintain his slim waistline and trim physique.

Harry said during a recent interview with The Sun that he consumes what he labelled as his own concoction called "bullet coffee." The drink reportedly helps him maintain his 26-inch waistline so he could fit into women's jeans. The 21-year old revealed this is his secret to ward off pangs of hunger and that he drinks it to replace his usual meals.

"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," he said.

Harry's fellow One Direction band mates also revealed that he likes to meditate when on the plane. So this is reportedly why they travel on different planes. Harry had also previously admitted to being a fan of Pilates, running and boxing.

Prior to consuming his bullet coffee, last year Harry had put green tea and sushi on his regular meals. A source told the Daily Star back in May last year that he would order this menu alongside his normal meals. The source claimed it was the "X-Factor UK" coach Nick Grimshaw who initially got him into the habit of eating sushi and drinking green tea for a healthy diet.

"Alongside the normal menus, Harry has put in his own special request of one sushi meal and five cups of green tea a day," the source said.

However, none of Harry's fellow One Direction band mates wanted none of his food. They even called it Harry's the "girlie food."

"They want none of the sushi and green tea, and find it funny he's asking their chefs to prepare what they consider girlie food. They all eat together at the same table - which has the same powder blue and white spotty tablecloth and napkins in every city. It helps give them a sense of routine and homeliness," the source further told the Daily Star.

Sarah Nicholas, the person in charge of One Direction's "Where We Are" tour told the publication then that Harry is such an "adventurous eater." While his band mates prefer their usual normal meals, the 21-year old "likes his Asian food and fish."