Potassium is a mineral that helps control the balance of fluids in the body, and also helps the heart muscle work properly. Potassium is found in most types of food. Fruit and some vegetables are a good source, especially bananas, broccoli, parsnips and brussels sprouts. Pulses, fish, shellfish, chicken, turkey and beef are also good sources. You should be able to get your recommended daily dose of potassium by maintaining a balanced diet.