Neither grapefruit nor grapefruit juice helps people to lose weight. Despite what many believe, the fruit does not have any fat-burning capabilities, according to WebMD.
Although some studies have shown that obese people who ate half a grapefruit before meals for three months lost considerably more weight than those who did not consume grapefruit juice or the fruit itself; experts suspect the water content made those people feel full, thereby reducing their urge to eat more solid food. Since the 1930s, many have claimed that grapefruit contains enzymes that help melt away fat. However, there is no scientific proof that this assertion is true.