What are calories?
Calories are a unit of energy. On food labels, they show how much energy the body can get from a food or drink to power everything from breathing to running.
The calories on food labels are actually kilocalories. One kilocalorie is the energy needed to raise the temperature of one kilogram of water by one degree Celsius. In many countries, food energy is also shown in kilojoules. One kilocalorie equals about 4.2 kilojoules.
The body gets calories from three main nutrients. Carbohydrates and protein provide about 4 calories per gram, while fat provides about 9 calories per gram. Alcohol provides about 7 calories per gram. Vitamins, minerals and water provide no calories.
Using energy
Even at rest, the body uses calories to keep the heart beating, breathe, maintain body temperature and repair cells. This is called the basal metabolic rate. Physical activity uses extra calories. If you take in more calories than you use, the body stores the extra, mostly as fat.
Did You Know?
The brain uses about 20 percent of the body's daily calories, even though it makes up only about 2 percent of body weight.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.