Believe it or not, people even in the 1930s were eating grapefruit — that contains certain enzymes and when eaten before other foods helps burn fat. Apparently, people going on a diet eating this fruit lost up to 10 pounds. But the real benefit of the fruit lies in the fact that it contains 92% water making it a good source of hydrating the body. A grapefruit a day may help lower bad lDl cholesterol levels and since it has plenty of Vitamins A and C in each serving, they boost immunity.