There are many versions of the Grapefruit Diet, which began in the 1930s as the Hollywood Diet. This diet claims that grapefruit contains a special fat-burning enzyme, activated when you eat half a grapefruit for each meal, along with small amounts of other food. Other versions vary in calories, with some as low as 800 per day.
Grapefruit is a good food, but so are other healthy foods like vegetables and other fruits.
There are several pitfalls to consider, however. Finally, to be healthy, we need a balance of foods from different food groups. The water weight comes back when a normal diet is resumed. Grapefruit can be part of a healthy eating plan, but because it's good food, not because it does anything special with burning fat. Kelly D. Brownell, PhD, is an internationally known expert on eating disorders, obesity, and body weight regulation.