For the vegetable sometimes called yam in the United States, see sweet potato. For the vegetable called yam in New Zealand, see Oxalis tuberosa. Yam is the common name for some plant species in the genus Dioscorea (family Dioscoreaceae) that form edible tubers. These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America, the Caribbean and Oceania. There are many cultivars of yam. Although some varieties of sweet potato (Ipomoea batatas) are also called yam in parts of the United States and Canada, it is not part of the family Dioscoreaceae but belongs in the unrelated morning glory family Convolvulaceae.
The true yam is a versatile vegetable. It can be barbecued, roasted, fried, grilled, boiled, baked, smoked and when grated it is processed into a dessert recipe
The protein content and quality of roots and tubers is lower than other food staples. Of all roots and tubers, the protein content of yam and potato is the highest, being approximately 2 percent on a fresh weight basis. Yams, with cassava, provide a much greater proportion of the protein intake in Africa, ranging from 6 percent in East and southern Africa to about 16 percent in humid West Africa.
Yam, like other root crops, is not a good source of essential amino acids. It is rich in phenylalanine and threonine but limiting in the sulphur amino-acids, cystine and methionine and in tryptophan. Yam consuming areas of Africa have a high incidence of kwashiorkor, a serious medical condition in children caused by protein deficiency. Experts emphasize the need to supplement a yam-driven diet with more protein-rich foods in order to support active and healthy growth in infants.
Except for potassium, vitamin B6 and vitamin C, yam is a food with moderate nutrient density. Yam provides around 110 calories per 100 grams. It has good levels of potassium, manganese, thiamin and dietary fiber, while being low in saturated fat and sodium. Yam generally has a lower glycemic index, about 54% of glucose per 150 gram serving, compared to potato products.