Carbohydrates are broken down in the body to become glucose, which gives us energy. Energy is measured in calories. We all need a certain number of calories each day for energy, even if we aren't very active. Just sitting in a chair we need energy to breathe. If there are too many calories in our diet we put on weight, and if there are too few we use up our body’s energy stores and lose weight. The amount of energy a person needs each day varies. It depends on how quickly their body uses the energy, and on their level of activity. An adult man needs about 2,500 calories a day and an adult woman needs about 2,000 calories.