When people eat more calories than they burn off, their bodies store the extra calories as fat.

A couple of pounds of extra body fat are not a health risk for most people. But when people keep up a pattern of eating more calories than they burn, more and more fat builds up in their bodies.

Eventually, the body gets to a point where the amount of body fat can have a negative effect on a person's health. Doctors use the terms "overweight" or "obese" to describe when someone is at greatest risk of developing weight-related health problems.

As you've probably heard, more people are overweight today than ever before. Experts are calling this an "obesity epidemic." This health problem affects young people as well as adults — one third of all kids between the ages of 2 and 19 are overweight or obese. So younger people are now developing health problems that used to affect only adults, like high blood pressure, high cholesterol, and type 2 diabetes.