Your body needs food for three main reasons: Food supplies the fuel for all the billions of cells in your body, and the raw materials to make new cells by cell division. Remember that cells divide to make new ones, not just for growth but also to replace damaged or worn out cells. Nutrients are the substances in food that your body can use. Get the balance right, and you are more likely to grow well and keep healthy. Get the balance wrong, and you will grow less, feel worse and possibly even become ill.