Calories = Energy When we talk about food giving our body energy we also need to talk about calories. Calories are units of energy that foods supply us. We need a certain amount of calories from our food, but not too many. Our bodies store extra calories that we do not use as fat. We need some fat, but not too much. We need to use the calories that we eat. Exercise is important for many reasons. One reason is that it burns calories so we do not store extra calories as fat. Remember to exercise at least 60 minutes a day.