Potato supplies complex carbohydrates that are essential for energy. One serving of a 5.3 ounce medium potato provides 10 percent of protein; 45 percent of the Recommended Daily Intake (RDI) for Vitamin C, most of which is found immediately under the skin; 21 percent of potassium and 3 grams of fiber. It has no fat and contains less than 100 calories. Potatoes are a very good source of Vitamin B6, potassium, copper, manganese, phosphorus, niacin, dietary fiber, and pantothenic acid. Potatoes also contain a variety of phytonutrients that have antioxidant activity. Among these important health-promoting compounds are carotenoids, flavonoids, and caffeic acid, as well as unique tuber storage proteins, such as patatin, which exhibit activity against free radicals.