Diets and diet books have never been more popular. At the same time, recent studies show that Americans have never been more overweight. It's no wonder, then, that women who are trying to lose weight--be it 10 or 100 pounds--are among the most frequently discouraged people around. Every day we are faced with fridge wars, bad mirror moments, diets that don't work, skinny friends who can eat whatever they like, and husbands who reminisce about the size 8 they married.

Yet victory can be yours. Increasingly, scientific...