Potassium performs many vital functions in the body. It helps nerves transmit messages, aids digestive enzymes, guides normal growth, and ensures proper muscle functioning, including that of the heart. Potassium is a major element in the fluid inside cells and plays an important role in maintaining the balances of water and acid in the body. Diuretic drugs, which may be prescribed for high blood pressure, cause potassium to be flushed out of the bloodstream, which can lead to a potassium deficiency. This also can occur with chronic diarrhea, vomiting, or kidney disease. People with eating disorders who misuse laxatives, diuretics, and who self-induce vomiting can get a potassium deficiency. Symptoms include paralysis, sterility, muscle weakness, mental apathy and confusion, and damage to the kidneys and heart. The best source of potassium is fresh fruits and vegetables, nearly all of which contain some potassium. Those high in the mineral include potatoes, bananas, tomatoes, oranges, dried peas, and dried beans, especially black and navy beans. Processed foods lose much of their potassium during processing. Next time you sweat a lot, in addition to drinking lots of water, try eating a high-potassium food, such as an orange.