One medium-sized plain baked potato (about three inches in diameter) has about 150 calories. That same potato has about five grams of fiber, which is important for a healthy digestive tract, and they're also a healthy source of vitamins and minerals.
A small baked potato has about 130 calories. A large baked potato can have about 275 calories. Toppings such as butter, sour cream and cheese will add more (sometimes a lot more) calories.
Potatoes contain more potassium than any other fresh vegetable in the produce department - even more than bananas. One potato has almost 900 milligrams, which is about 20 percent of what you need every day.
Potassium is important for body growth and cell maintenance. It's also necessary for nervous system function and normal muscle contraction - including the heart muscle. Potassium is also an electrolyte that helps balance the fluids in your body, which is important for healthy blood pressure.
Vitamins and Health Benefits
Potatoes also contain substantial amounts of vitamins C and B-6, which are vital for blood clotting, wound healing, a strong immune system, normal nervous system function and for converting the food you eat to energy. Potatoes also contain a substance called kukoamine that may help to lower blood pressure, although more research is necessary to know for sure.
Source: United States Department of Agriculture National Nutrient Database for Standard Reference. "Potatoes, raw with skin and salt." Accessed August 29, 2011. http://www.nal.usda.gov/fnic/foodcomp/search/.