There’s been much buzz in women’s health circles about food and fertility. Books like The Infertility Diet by Fern Reiss suggest that eating a balanced diet that includes certain key foods can help women get pregnant and prevent miscarriage. One of the foods receiving a flurry of attention is the yam. Research conducted at Yale University linked the high consumption of white yams among the Yoruba people in Nigeria to that society’s high incidence of fraternal twins. These yams contain unique compounds called diosgenins, which may have an impact on hormonal patterns, thereby increasing ovulation.
What's the Difference?
Here in America, the very word "yam" can be cause for confusion. In the grocery store, there are often two different types of similar-looking elongated tubers, one marked sweet potato and one marked yam. However, as it turns out, the yams in American produce aisles are not true yams — they are simply a second variety of sweet potatoes. True yams are native to Africa and rarely found in American markets, except in specialty Asian and African stores. They often have brown or black skin with off-white, purple, or red flesh. Much starchier than sweet potatoes, they have an earthy, rather than sweet, taste. True yams and sweet potatoes are not even distantly related; they come from two different plant families. The confusion between the two originated in the Southern United States, where the African word for true yams, "nyami," was applied to the orange-fleshed sweet potatoes to distinguish it from other varieties.
Sweet for a Reason
So, eating American “yams” (which are really sweet potatoes) will not impart the fertility benefits experienced by the Yoruba people in Africa. Still, that doesn’t mean the sweet potato, native to Central America, is devoid of health benefits — far from it. The moist-fleshed, orange-hued sweet potato was ranked by the Center for Science in Public Interest as having the highest nutritional value compared to a host of other vegetables. Its vibrant color is a clue to its high concentration of Vitamin A in the form of beta-carotene. One sweet potato contains five times the recommended daily allowance of Vitamin A, a powerful antioxidant that protects against free radicals and helps guard against smoking-related diseases like emphysema and lung cancer. Sweet potatoes are also a good source of Vitamin C and the trace mineral manganese.
Though they may taste as sweet as candy, sweet potatoes have a positive effect on blood sugar. With high concentrations of fiber, complex carbohydrates and carotenoids, they help stabilize blood sugar levels. Because they also lower insulin resistance, they are thought to have anti-diabetic properties. The substantial fiber content lowers the risk of cancer and heart disease as well.
True African yams are lower in Vitamins A and C than sweet potatoes, but they are an excellent source of Vitamin B6, which reduces the risk of heart disease by breaking down a compound that can damage blood vessels. Yams have a long history of use in traditional herbal medicine to help regulate organ system function. Wild yam cream, topically applied, has been touted as a natural alternative to hormone replacement in menopausal women, though there are no scientific studies proving its efficacy. Still, as the fertility research among the Yoruba has demonstrated, we have much to learn about the complex effects of yams on the female hormone system.
By any name, then, these unrelated but oft-confused tubers offer distinctive health benefits that have stood the test of time. Sweet potatoes, consumed since prehistoric times, are one of the oldest vegetables on earth, while yams have been cultivated in Asia and Africa since 50,000 B.C., a testament to these tubers’ delicious taste and contribution to well-being.