Chances are, you've either heard of or been on one of the countless fad diets that promise instant results, from the cabbage soup diet to the grapefruit diet and beyond. Recently, three Oprah Radio staffers tested a fad diet known as "the three day diet," which claims that followers will lose 10 pounds if they drastically cut their caloric intake and skip snacks for three days.

Rita, Leslie and Annette say they did indeed lose some weight on the three day diet, but after Bob grills the women, he concludes that this fad diet—and all the others out there—fall short. Here's why:

• Fad diets distort the true meaning of the word "diet," which is simply the foods you eat. "Diet should not mean what it has come to mean, which is a temporary way of eating for a temporary result," Bob says.
• Fad diets lack nutritional value. Bob says the fad diet his colleagues followed was "nutritionally void," and lacked calcium, fiber and whole grains, among other things.
• Oftentimes, fad diets are too high in sodium, Bob says. The diet he critiqued included high-sodium crackers with no nutritional value.
• Fad diets are often too low in calories. Bob says he'd rather see an individual exercising more and upping their caloric intake instead of depriving themselves.
• Fad diets rely on gimmicks, rather than common sense. Hot dogs and ice cream served as the hook for this particular diet, both of which Bob says should only be eaten sparingly.
• The pounds you lose on a fad diet are mostly water weight.
• You can't reasonably stay on a fad diet for an extended period of time. "They'll work temporarily, but you can't live this way," Bob says.