Boiled in its skin, a large potato, weighing about 300 grams, has 261 calories, 5.6 grams of protein and .3 grams of fat. If you peel the potato before boiling it, you lose about a half gram of protein, but the calorie and fat contents remain similar. Peeled or unpeeled, the potato has 5.4 grams of fiber, about the same amount as a bowl of bran flakes cereal, and 2.6 grams of natural sugar.
B-Complex Vitamins and Vitamin C
A large, unpeeled boiled potato is rich in B-complex vitamins, which help your body form blood cells and make energy from the protein, carbohydrates and fat from the food you eat. A boiled potato provides more than half of the vitamin B-6 you need each day, as well as about 30 percent of your recommended daily intake for thiamin and niacin. It is also high in vitamin C, giving you one-half of your daily requirement for that nutrient. A peeled boiled potato loses half of its vitamin C content and provides 25 percent of the vitamin C you need daily.
Magnesium, Phosphorus and Potassium
Because the potato is a root vegetable, it is rich in essential minerals that help you build strong bones and benefit your nerve and muscle function. A large potato, boiled in its skin, provides 1.1 grams of potassium, one-fourth of the potassium you need daily. It also gives you about one-fifth of the magnesium and phosphorus you need each day. If you peel the potato before boiling it, the potato loses some of its mineral content, providing one-fourth of the potassium and one-sixth of the phosphorus you need daily.
Cooking a potato in water depletes it of some of its nutrients. A baked potato is more nutrient-dense, providing 6.28 grams of protein and 6.3 grams of fiber. It has about 25 percent more magnesium as a boiled potato. It also contains 40 percent more phosphorus and potassium, as well as four times the amount of folate in a boiled potato. Pregnant women, who need an adequate amount of folate to prevent neural tube birth defects in their unborn children, benefit from eating potatoes baked, rather than boiled.
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