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Yams nutrition facts

Yams are staple tuber vegetables of West African origin. There is lot of ritualism and symbolism has been associated with this humble starchy root vegetable all over Africa, Asia and Latin Americas.

Botanically they belong to the family Dioscoreaceae; of genus Dioscorea. There are several hundred species of Dioscorea exist; however, some of commercially important varieties of yam tuber are Dioscorea rotundata (white guinea), D. alata (yellow), D. bulbifera (aerial), D. opposita (chinese), D. esculenta (south east asian) and D. dumenterum (trifoliate).

Yam tubers (Dioscorea rotundata) put for sale in a market. (Photo courtesy:  Nick Hobgood)	Chinese yams (D. opposita).  Note for small size, club shaped tubers. Photo cortesy: Jason Doucette

The plant is a perennial vine cultivated for its large, edible, underground tuber, which can grow up to 120 pounds in weight and up to 2 meters in length. They are the tropical crops and never grow where the temperature dips below 68 degrees F.

Yam is similar in appearance to sweet potato; but not at all related to it. Important differences: yams are monocotyledons, larger in size, features thick, rough, dark brown to pink skin depending up on cultivar type whereas sweet potatoes (Ipomoea batatas) are dicotyledonous, relatively smaller in size and possess very thin peel. 

Although the tuber is grown throughout Africa, Nigeria is the world’s largest producer and exporter of yam, accounting for over 70 percent of the world total output.

Health benefits of yams

• Yam is a good source of energy; 100 g provides 118 calories.  It mainly composed of complex carbohydrates and soluble dietary fiber. Together, they raise blood sugar levels rather very slowly than simple sugars and therefore recommended as low glycemic index healthy food. In addition, dietary fiber helps reduce constipation, decrease bad or "LDL" cholesterol levels by binding to it in the intestines and prevent colon cancer risks by preventing toxic compounds in the food from adhering to colon mucosa.

• The tuber is excellent source of B-complex group of vitamins. Provides adequate daily requirements of pyridoxine (viamin B6), thiamin (vitamin B1), riboflavin, folic acid, pantothenic acid and niacin. These vitamins mediate various metabolic functions in the body.

• Fresh root also contains good amounts of anti-oxidant vitamin, vitamin-C. Provides about 29% of recommended levels per 100 g.  Vitamin C has important roles in anti-aging, immune function, wound healing, bone growth.

• Also contains good amount of vitamin-A and beta carotene levels. Carotenes coonvert to vitamin A in the body. These compounds are strong antioxidants. Vitamin A has many functions like maintaining healthy mucus membranes and skin, night vision, growth and protection from lung and oral cavity cancers.

• This tuber is indeed one of the vegetable rich sources of minerals like copper, calcium, potassium, iron, manganese and phosphorus. 100 g provides about 816 mg of Potassium. Potassium is an important component of cell and body fluids which helps controlling heart rate and blood pressure by countering hypertensive effects of sodium. Copper is required in the production of red blood cells. Manganese is used by the body as a co-factor for the antioxidant enzyme superoxide dismutase. Iron is required for red blood cell formation.

Selection and storage

Yams are available in the markets year around. Fresh tubers, however, are available in plenty by August when the annual harvest season begins at the end of rainy season in western Africa. A new yam festival celebrated in symbolism to fresh crop and availability of fresh food in abundance all over Nigeria and Ghana with great fervor.

In the super-markets generally you find small cut sections wrapped in thin plastic covers. Their interior meat is white to light pink in color depending up on cultivar type with rich starchy flavor. 

In general, whole tubers are stored after drying several hours in a well ventilated yam barn where they keep well for several months without refrigeration. Cut sections, however, are used early or stored in the refrigerator for immediate use.

Preparation and serving methods

Unlike sweet potatoes which can be eaten raw, yams should not be eaten raw since they contain many naturally occurring plant toxins including dioscorin, diosgenin and tri-terpenes. They must be peeled and cooked in order to remove these bitter proteins.

Here are some serving tips:

• The tuber can be used in variety of cuisines either boiled, baked, or fried, sometimes roasted.

• The most common cooking method in Africa is "pounded yam". Fufu (Foo-foo, Foufou) is a special dish prepared during yam festival. To make fufu: either pounded yam or its powder is added to boiling water to make a cake like mass. A bite-sized piece of the fufu is torn from cake and consumed with sauce, stew or soup akin to ragi millet cake eaten in some parts of south India.

• Japanese yam or yamaimo is eaten raw as salads or grated to get gel like milk which is added to noodles.

• It is also used like sweet potatoes in the preparation of cake, casseroles, breads etc.

Medicinal uses

Yam tubers are used various traditional medicines in China, Korea and Japan. The mucilaginous tuber milk contains allantoin, a cell-proliferant that speeds the healing process when applied externally to ulcers, boils and abscesses. Its decoction is also used to stimulate appetite and to relieve bronchial irritation, cough etc.

Safety profile

Yams of African species must be cooked to be safely eaten, because various natural toxin substances such as dioscorine can cause illness if consumed. (Medical disclaimer)

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