Diets are not just for getting slim. You need a varied and healthy diet (not necessarily a slimming diet) to stay healthy, whatever shape you may be. A proper mix of foods will give you all you need for healthy growth.

You need regular exercise, too. Exercise helps keep you fit. When you exercise, your muscles work harder. Exercise makes your heart work harder, pushing blood to your muscles. Your pulse rate - the throbbing in your wrist - is caused by the blood being pushed round your body.

Some chemicals can change your body and the way it behaves. These special chemicals are called drugs. Most drugs are medicines, and they are used to treat illnesses and their symptoms. But there are some drugs that people use to change their bodies that can harm them and that may become addictive. People like the change so much that they want to take the drug again and again. These drugs include tobacco - the material in cigarettes - and alcohol.