The “Grapefruit Diet” (also known as the Hollywood Diet and Mayo Diet) has been around since at least the 1930s. The ideal is that something inside a grapefruit – some magical enzyme – can burn fat. The problem of course is that there is no scientific proof that this magical ingredient exists. Yes, people do lose weight when following the grapefruit diet, but they regain it almost immediately after they go off it. That’s because the grapefruit diet (so-called because it includes drinking grapefruit juice at every meal) is what’s known as a Very Low-Calorie diet – that is, a…