Ask the doctor: How you burn calories matters when you're trying to lose weight

Q. Is it true that losing weight is mostly a matter of calories in, calories out?

A. For the first 30 years of my life, I was slim. But in my 30s, I started to gain weight. My doctor told me just what I would have told one of my patients: "It's simple: you have to burn off with exercise more calories than you've eaten. You need to exercise more or eat less. Your weight problem is a problem of willpower."