Harvard Health Letter

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."

It is true and always will be true that exercising more and eating less can help you lose weight, and that doing so requires willpower. However, in the past several decades we have discovered that losing weight is a lot more complicated than that.

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