Transcript: The Grapefruit Diet has been around for years, but its premise hasn't changed. Grapefruit contains plant compounds that are believed to balance levels of the hormone insulin, thereby kick-starting metabolism. Perhaps the best part about the Grapefruit Diet is its length: Twelve days of dieting and you're done! This means that the diet is best for people wishing to lose a little weight in a short time-like those red carpet regulars! The Grapefruit Diet involves, of course, eating grapefruit at every meal.  It also stresses lots of black coffee-which is said to help speed metabolism-and minimal calories. ….Only 800 calories to be exact, which is about half of what a sedentary 130 pound woman needs each day! So while dieting like a Floridian might leave you hungry, it may also leave you up to 12 pounds lighter!