Paparazzi shots regularly show Hollywood’s skinniest actresses, such as Renee Zellweger and Mary-Kate Olsen, sporting giant sunglasses and regularly coming out of Starbucks clutching gigantic cups of coffee.

This is a trend in Hollywood, where many believe coffee not only speeds up their metabolism but also keeps them from eating. “One client I had would eat almost nothing all day, she just drank coffee constantly,” says trainer to the stars Peterson. “She’d have some lettuce in the afternoon, and drink coffee instead of dinner. Working out was a waste of time because of the state she was in.”

Marc David says: “Coffee and caffeine can actually make you fat. If you’re drinking too much, the caffeine mimics the stress response in our bodies and your cortisol and insulin levels rise. These elevated levels of stress hormone signal the body to store fat.”