"Some don't feel successful. They feel they have to lose so much more weight and reach that ultimate goal - their 'dream weight,' " said Dr. Robert Kushner, a professor at Northwestern University and author of "Dr. Kushner's Personality Type Diet."

That goal is often unrealistic, like when a 42-year-old wants to get down to his or her weight in high school, Kushner said.

Some women who lose a little weight are so disappointed with their still-not-buff bodies, they become "exercise addicts," said Debbie Mandel, a lecturer at Brooklyn College and author of "Turn on Your Inner Light: Fitness for Mind, Body and Soul."

Susan Edelman