Maybe not, says Harvard University scientist Richard Wrangham, who believes that many of the official numbers are wrong. "Where foods are highly processed, such as white bread or a Twinkie, the calories on the package are probably reliable," he says. "But for less processed foods, you're probably getting fewer calories than the official caloric value." Wrangham thinks some numbers may be off by 30 percent or more.

That's because the calories listed on labels are determined by a method that ignores whether the food has been processed, cooked, or otherwise made more easily digested. Wrangham says the physical structure of food influences how much of it the body absorbs. Foods that are harder to digest, like chewy whole grains or