Sweet potatoes and "true yams" are totally different vegetables from two separate botanical families. Sweet potatoes, which originated in the tropics of Peru and Equador, are roots from the species Ipomoea batatas and belong to the Morning Glory family (Convolvulaceae). True yams, which originated in Africa, are from the Dioscorea genus (Dioscoreaceae family) and aren't as nutritious as sweet potatoes. They aren't grown in the United States because they require a much longer growing season, but are imported through the Caribbean. True yams have a rough, scaly brown skin and are very low in Beta-Carotene. Sweet potatoes usually have a smooth orange skin and are high in Beta-Carotene. Place them side by side and you can plainly see the difference.
In some parts of the Asian and West African tropics, true yams are the staple food. So important to the people of Fiji that their eleven-month calendar is based on the vegetables growth cycle. On some islands, the size and quality of the familys yams are extremely important. After the harvest, their yams are put on display as neighbors come to admire their gardening skills. Long lines of men and women proceed with the men carrying the prized yams into the village where piles line the streets as families display their pride and joy. The yam is so prevalent in these regions that many roots are called by its name. Inedible yams serve other purposes such as to poison darts.Yam bean is a name applied to several species of edible tubers, seeds and pods.
Today, the birth-control pill is derived from true yams. Dr. John Lee, author of What Your Doctor May Not Tell You About Menopause, explains how manufacturers take diosgenin from the Wild Mexican Yam to make progesterone. From that they create a substance called progestins ,the basis of birth control pills. Dioscorea is a natural precursor of DHEA, known for helping to normalize hormone production in women over age 30. As we age our bodies produce less DHEA. Loss of DHEA levels in the body results in a loss of energy and reduced immune system function. Wild Mexican Yam extract (containing "active" Wild Mexican Yam from Dioscorea) is also an important ingredient in a natural progesterone cream used to treat menopausal and PMS symptoms in women. And, many researchers now believe that the progesterone derived from true yams may aid in normal bone building in females good news for women concerned about osteoporosis.
Today about 9 million American women take some form of Premarin for menopausal symptoms, the most common drug used for estrogen replacement therapy (ERT). Premarin, which is short for "Pregnant Mares Urine," is a method of ERT that was introduced in 1942 before natural and synthetic alternatives were available. Natural progesterone and natural estrogen are important plant hormones almost identical to what our bodies excrete. In his second book, "What Your Doctor May Not Tell You About Breast Cancer," Dr. Lee says that, "Natural progesterone is virtually the same module as the progesterone the female body makes." which he says protects against breast cancer.
There are many other effective FDA approved estrogen-replacement drugs on the market today. These alternatives, which are derived from plant or synthetic estrogens, are a close replica of human estrogen without animal impurities. They're made from various vegetable sources such as beets, soy beans, sweet potatoes and true yams. Although industry officials claim that lab produced substances costs twice as much to produce, there are companies who successfully market these alternatives. To name a few: Estraderm made from sweet potato is made by CIBA Specialty Chemicals, Ogen made from various vegetables is made by Upjohn, Estrace made from yams and soybeans is made by Mead Johnson, a division of Bristol-Myers Squibb.
The African word nyami, referring to true yams, means to eat and is a term that was adopted in its English form of yam. But, what are referred to as yams in the United States are actually sweet potatoes with a relatively moist texture and orange flesh. It is generally thought that the yam is a more moist sweet potato though varieties vary in degrees of moistness. Although the terms sweet potatoes and yams are generally used interchangeably, the United States Department of Agriculture requires that they be labeled as sweet potatoes.
Several decades ago when orange fleshed sweet potatoes were first introduced in the southern United States, producers and shippers desired to distinguish them from the more traditional yellow and white flesh dry types. The Yellow Jersey is a dry type of sweet potato whereas the Centennial, Jewel and others are more moist types of sweet potatoes. The latter are what we refer to as yams. The Jersey type, one of the two types of sweet potatoes produced for food in the United States, has a dry flesh, remains dry and firm when cooked and is less sweet than the moist-fleshed variety. People from Louisiana have always called their sweet potatoes yams. While at one time there was a lack of agreement in what variety of sweet potatoes should or should not be called yams, this is no longer the case. Today the word yam is used as a trademark among produce wholesalers and retailers to identify orange types or Louisiana sweet potatoes soft, moist and sweet when cooked with a deep orange or copper color skin.
Several varieties make up each of the two types. One variety
of the moist-fleshed type is the Centennial. Developed by the Louisiana
Agricultural Experiment Station, it has a bright copper skin and a deep orange
flesh, denoting an abundance of Beta-Carotene (Vitamin A). Another popular
variety is the Beauregard, also with a bright copper skin and a deep orange
flesh that was developed by the late Dr. Julian Miller and his associate
horticulturists at Louisiana State University. The canned and frozen yams
found in food stores are also sweet potatoes. The flesh turns soft, moist
and sweet during cooking. The skin of the more popular varieties of the
dry-fleshed or Jersey type is yellowish or pale brown in color. The skin
of this type may vary from pale yellow to yellow to light brown, depending
on the variety.
Information provided in part by the following:
Drs. Jonathan R. Schultheis and L. George Wilson, Extension Horticultural Specialists, Department of Horticultural Science, North Carolina Cooperative Extension Service, North Carolina State University, P.O. Box 7609, Raleigh, NC 27695-7609.
Ms. Sue Johnson-Langdon, Executive Director, North Carolina SweetPotato Commission, Inc., 1327 Bright Leaf Blvd., Suite H, Smithfield, NC 27577, (919) 989-7323, (919) 989-3015 (fax).
Louisiana Sweet Potato Commission, Division of Louisiana Department of Agriculture, P.O. Box 3334, Baton Rouge, LA 70821-3334, 504) 922-1277, (504) 922-1289 (fax).
Sweet potato (yam) and yam graphics used with permission.
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Article from "The Joy of Cooking With