Assists in the regulation of the acid-base balance and water balance in the blood and the body tissues. It assists in protein synthesis from amino acids and in carbohydrate metabolism. It is necessary for the building of muscle and for normal body growth. Potassium is also needed for the proper functioning of nerve cells, in the brain and throughout the body.Fish such as salmon, cod, flounder, and sardines are good sources of potassium. Various other meats also contain potassium. Vegetables including broccoli, peas, lima beans, tomatoes, potatoes (especially their skins), and leafy green vegetables such as spinach, lettuce, and parsley contain potassium. Fruits that contain significant sources of potassium are citrus fruits, apples, bananas, and apricots.