Most Americans eat far too much, he says. A one-cup serving of vegetables or fruit is about the size of a baseball. A recommended 3-ounce serving of meat, fish or poultry is the size of a deck of cards. Yet many Americans have become accustomed to eating much larger portions. This is nonsense, says Karas.
Few people have radically slow metabolisms, a rare medical condition.
While everyone's metabolism varies, the difference is largely a factor of how much lean-muscle mass we carry. Building muscle increases metabolism and you are never too old to do it, Karas says. Someone who adds five pounds of muscle can burn an additional 250 calories a day. If they keep that muscle on for one year, they will burn a total of 91,250 extra calories. The cardiovascular exercise that many people do is not helpful in losing weight, Karas says.