We need calories or energy to do the things every day. For example, when we walk or ride a bike to school, we spend a certain amount of calorie and even when we sleep, we also use them. But how many calories should we spend a day to stay in shape? It's difficult for us to calculate. If people want to keep fit, they should remember that everyone should have between 1600 and 2500 calories a day. We get calories in the food we eat. If we get too much food and don't take part from any activities, we can get fat quickly. But if we don't eat enough, we feel tired and weak.