While yams appear very similar to sweet potatoes, they're quite different. In fact, they're not even related. Yams belong to the Dioscoreae or morning glory family, while sweet potatoes are from the genus Convolvulaceae. Yams (from the African word "nyami," meaning "to eat") have only one embryonic seed leaf, while sweet potatoes have two.
Yams are grown throughout Africa, but Nigeria is the world’s most prolific producer, exporting to 70% of the world market. Close to 200 species of yams are eaten worldwide, but other than those found wrapped individually in supermarkets, they aren't easily found on American produce shelves. Popular varieties include Hawaiian yam, Korean yam, and sweet yam.
Compared to sweet potatoes, yams are usually longer – sometimes as long as several feet – and not as sweet, having a rough, dark orange or brown surface that looks like tree bark. They're usually harvested after a year of vine growth, dried for several hours in a barn ventilated for that purpose, after which they can be stored without refrigeration for several weeks.
Yam varieties are classified as either "firm" or "soft." When cooked, the former are more dense; the latter varieties become more tender and moist. Preparations can be as vast the varieties, including boiling, mashing, grilling, roasting, baking, or sautéing.
Yams should never be refrigerated until they're cooked. Leftovers should be wrapped, refrigerated, and eaten within a few days.
Health Benefits of Yam
Although they're considered to be a starchy vegetable, yams are made up of complex carbohydrates and dietary fiber allowing for slow uptake to keep blood sugar levels even, giving it the nod as a low glycemic index food. The vitamin A that is converted into beta-carotene when eating yams isn't as spectacular as those in sweet potatoes, but the antioxidants they provide are exceptional. The vitamin A in yams has other functions, such as maintaining healthy mucous membranes and skin, heightening night vision, supporting healthy bone development, and providing protection from lung and mouth cancers.
Yams are a good source of vitamin C – 27% of the daily value for fighting infections such as colds and flu and quick wound healing, anti-aging, strong bones, and healthy immune function. It also provides good amounts of fiber, potassium, manganese, and metabolic B vitamins. The content of vitamin B6 (pyridoxine; 16% of the daily value) is good for shrinking the effects of homocysteine, which can do real damage to cell walls that could lead to heart attacks and/or stroke.
Other nutrients in yams include thiamin (vitamin B1), riboflavin, folic acid, pantothenic acid, and niacin. Copper (which produces healthy red blood cells), calcium, potassium (supporting optimal cell and body fluids), iron, manganese (a component in the super-potent antioxidant enzyme superoxide dismutase), and phosphorus are body-beneficial minerals found in yams.
Chinese, Korean, and Japanese medicine has made use of yams for eons because they contain allantoin, although that wasn't always known. This compound speeds up the healing process when applied as a poultice to boils and abscesses, but is also used to stimulate appetite and relieve bronchial trouble.
Unless they're peeled and cooked, yams may contain toxins such as dioscorin, diosgenin, and tri-terpenes that you don't get from sweet potatoes, so handle them with care.
Yam Nutrition Facts
Serving Size: 3.5 ounces (100 grams), raw
|Calories from Fat
*Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie
Studies on Yam
There's an interesting link between yams and unpleasant menopausal symptoms. Wild yam extracts have been studied as a possible remedy, due to steroidal saponin compounds, but there's been nothing conclusive so far. Among the saponin compounds is a chemical known as diosgenin, which tests have shown to exert a positive impact on hormonal patterns, and possible benefits for lowering the risk of osteoporosis.1
One yam variety, Dioscorea bulbifera, was found in another study to improve ventricular function and protect the tissues surrounding the heart.2 Tests on yams are ongoing.
Yam Healthy Recipes:
Yam "Chips" with Cinnamon and Nutmeg
|2 large yams, peeled and sliced ¼-inch thick
||Olive oil, to drizzle
||1 tablespoon ground cinnamon
|1 teaspoon grated nutmeg
||Honey, to drizzle
- Preheat oven to 450°F.
- Place sliced yams in a rectangular glass dish. Drizzle lightly with olive oil. Sprinkle with cinnamon and nutmeg. Drizzle with honey. Place in oven for 20 minutes.
- Allow to cool slightly before serving. Makes four servings.
(From Healthy Recipes for Your Nutritional Type
by Dr. Mercola)
Yam Fun Facts
Yams are thought to have originated in Asia, carried to Africa around the first century before being transported to the Caribbean with the slave trade.
Thought to be one of the world's earliest vegetables under cultivation, yams may be undergoing an identity crisis due to frequent comparison with sweet potatoes. Though yams don't come close to the vitamin A content and carotenoid presence, this world-traveling tuber has a unique set of phytonutrients. Besides strong antioxidants, including the enzyme superoxide dismutase, yams contain vitamin C, fiber, potassium, manganese, B vitamins, and a long line of other minerals like riboflavin, potassium, iron, and manganese.
Yams, which may have a role in stabilizing hormonal patterns and lowering risk of osteoporosis, shouldn't be refrigerated before they're cooked. Recipes can swing to the sweet or savory side, depending on your desire. But either way, it generally commands a second helping.