Many teenagers don't have a healthy diet. They eat too much fat, sugar and salt, and not enough fruit, vegetables and fibre. This can lead to health problems in later life such as heart disease, cancer and diabetes. Teenagers are still growing and need energy for their bodies to grow properly. But they can get too many calories from foods that are high in fat and sugar. These foods usually have little or no fibre, so they don't fill you up for very long. If you eat these foods regularly without eating meals with lots of fibre and veg, you will probably become overweight or obese. This can be a problem because being overweight or obese increases your risk of developing many serious diseases like type 2 diabetes, heart disease, stroke and some cancers. It also makes it harder for your body to fight infections such as asthma and bronchitis (chronic lung disease).