Potatoes are an important food source.  They are the most widely cultivated vegetable in the world. An average-sized potato weighing between 6 and 8 ounces contains fewer than 100 calories.  Potatoes consist of about 80 percent water, 20 percent solid matter and have a high nutritional value.  Starch makes up about 85 percent of this solid mass and the rest is protein. Potatoes provide vitamins including niacin, riboflavin, thiamin, and vitamin C.  They also contain minerals such as calcium, iron, magnesium, phosphorus, potassium, sodium, and sulfur.