When people talk about the calories in food, what do they mean? A calorie is a unit of measurement — but it doesn't measure weight or length. A calorie is a unit of energy. When you hear something contains 100 calories, it's a way of describing how much energy your body could get from eating or drinking it.

Are Calories Bad for You?

Calories aren't bad for you. Your body needs calories for energy. But eating too many calories — and not burning enough of them off through activity — can lead to weight gain .

Most foods and drinks contain calories. Some foods, such as lettuce, contain few calories (1 cup of shredded lettuce has less than 10 calories). Other foods, like peanuts, contain a lot of calories (½ cup of peanuts has 427 calories).

You can find out how many calories are in a food by looking at the nutrition facts label. The label also will describe the components of the food — how many grams of carbohydrate, protein, and fat it contains.

Here's how many calories are in 1 gram of each:

· carbohydrate — 4 calories

· protein — 4 calories

· fat — 9 calories

That means if you know how many grams of each one are in a food, you can calculate the total calories. You would multiply the number of grams by the number of calories in a gram of that food component. For example, if a serving of potato chips (about 20 chips) has 10 grams of fat, 90 calories are from fat. That's 10 grams x 9 calories per gram.

Some people watch their calories if they are trying to lose weight. Most kids don't need to do this, but all kids can benefit from eating a healthy, balanced diet that includes the right number of calories — not too many, not too few. But how do you know how many calories you need?

How the Body Uses Calories

Some people mistakenly believe they have to burn off all the calories they eat or they will gain weight. This isn't true. Your body needs some calories just to operate — to keep your heart beating and your lungs breathing. It is a great idea to play and be active for at least 1 hour and up to several hours a day. That means time spent playing sports, just running around outside, or riding your bike. It all adds up. Being active every day keeps your body strong and can help you maintain a healthy weight.

Watching TV and playing video games won't burn many calories at all, which is why you should try to limit those activities to 1 to 2 hours per day. A person burns only about 1 calorie per minute while watching TV, about the same as sleeping!