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Learning About Calories

Medically reviewed by: Mary L. Gavin, MD

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 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. 

Water has no calories, but most foods and drinks contain calories. Some foods, such as lettuce, have few calories (1 cup of shredded lettuce has less than 10 calories). Other foods, like peanuts, contain a lot of calories (1/4  cup of peanuts has about 200 calories). High-calorie foods — such as sugary sodas, candy, and fast food — can quickly add up to too many calories. When you eat more calories than the body uses, the extra energy is stored as fat.

Some people watch their calories if they are trying to lose weight. Most kids don't need to count calories, but all kids benefit from eating a healthy, balanced diet. Kids should also pay attention to when they feel hungry and stop eating when they feel full.

How the Body Uses Calories

Your body needs calories to operate — to keep your heart beating, your lungs breathing, and your brain thinking. As a kid, your body needs calories and nutrients from a variety of foods to grow up.

Your muscles use calories to move. Being active every day keeps your body strong and can help you have a healthy weight. Aim for 1 hour or more of physical activity every day. You can be active playing outside, walking, riding your bike, swimming, dancing, or playing sports. 

How Many Calories Do Kids Need?

Kids come in all sizes, and each person's body burns energy (calories) at different rates. So there isn't one perfect number of calories that every kid should eat. The number of calories kids need depend on many things, like:

  • Age: Older kids need more calories than younger ones.
  • Gender: Boys tend to need more calories than girls, especially after puberty.
  • Height and weight: The bigger you are, the more calories you need.
  • Puberty: Because puberty is a time of fast growth, the body needs more calories.
  • Physical activity: Kids who are active need more calories than kids who don’t move as much.

Eating more calories than your body needs can lead to being overweight and other health problems. Only your doctor can say if you are overweight, so check with them if you're concerned. And never go on a diet without talking to the doctor first!

Medically reviewed by: Mary L. Gavin, MD
Date reviewed: November 2021