The many varieties of sweet potatoes add to the confusion about which type offers the best nutrition. Often called yams in the U.S., sweet potatoes offer better nutrition than true yams. True yams -- often white-fleshed -- provide little Vitamin A, but sweet potatoes offer high amounts of this vitamin. White sweet potatoes yield less beta-carotene, the form of Vitamin A that gives orange-fleshed varieties their distinctive color.
Nutritional Benefits
One medium sweet potato weighing 114 g provides 105 calories. The potato contains 2.29 g of protein, 0.17 g of fat, and 23.61 g of carbohydrate. The potato also offers 3.8 g of dietary fiber. A medium sweet potato holds 28.4 percent of the Daily Value of Vitamin C and 12.5 percent of the DV for Vitamin B6. Sweet potatoes provide significant amounts of important minerals including manganese, copper, potassium and iron. Vitamin A tops the list of nutrients in sweet potatoes but only the orange-fleshed varieties provide unusual amounts. Orange types yield as much as 262.2 percent of the DV of Vitamin A as beta-carotene. As color fades towards white, the beta-carotene contents falls.
Varieties
White sweet potatoes popular in the American South yield a sweet flesh with a drier texture than orange fleshed varieties. Most white sweet potatoes require a longer growing season to produce the best yields. White varieties may be confused with true yams, which also have white flesh, but the two plants come from different families completely. True yams grow only in tropical climates and may reach harvest weights of 100 pounds. White sweet potatoes suitable for temperate climates include Southern Queen or O'Henry. Growers in subtropical Florida prefer boniato for its drier lighter texture and reduced sweetness.
Misconceptions
Most sweet potatoes and yams sold in the U.S. actually belong to the same morning glory family of plants. The term yam became a popular marketing term in the U.S. and helped distinguish the orange-fleshed types from the older white and yellow varieties. True yams found in specialty markets show a rougher scaly skin than sweet potatoes do, and taste starchy and dry rather than moist and sweet. True yams don't provide high amounts of Vitamin A.
History
The sweet potato originated in Central America. Evidence of sweet potato consumption dates back at least 10,000 years to ancient Peru, making this one of the oldest known vegetable crops. Brought back to Europe by Christopher Columbus after his first journey to America, the sweet potato quickly spread to other parts of the world. Orange-fleshed varieties now make up the bulk of the sweet potato harvest in the U.S. but were only introduced in the middle of the twentieth Century. Both Native Americans and early settlers grew white and yellow varieties.
Potential
In developing countries where Vitamin A deficiency causes many health problems including blindness and death, replacing white-fleshed true yams with orange-fleshed sweet potatoes could literally save lives. White sweet potato varieties may also provide true health benefits, however. According to North Carolina State University, the Japanese use white sweet potatoes as a natural treatment for diabetes, hypertension and anemia. A dietary supplement called Caiapo, developed from the potato's peel by Japanese scientists, may help control blood glucose levels in diabetics.
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