These three nutritious tubers are not identical. Some Yoruba attribute frequent twins to one, the yam. Why not eat some to ring in the year? All three are gluten-free.
These three tuberous root vegetables – yam, sweet potato, taro root – hail from different families but are similar to, and can sometimes be substituted for one another.
All are high in fiber, potassium, manganese, and some B vitamins including B6, and relatively low in fat. And all have a low glycemic index (which means they do not raise your blood sugar excessively). They are also low in protein, particularly the amino acid lysine. And all are of course gluten-free.
Both yam and taro must be well cooked, as these can be toxic raw. The yam's skin requires extra care as it sometimes causes rashes (which are treated in Africa with palm oil). The sweet potato is not quite so toxic, but nevertheless should be cooked, since when raw an enzyme inhibitor in it blocks digestion of proteins (cooking deactivates this).
While most yam varieties (with white or purple flesh) are not rich in caratenoids, most varieties of sweet potato are. Although not one of the original three sisters, sweet potatoes may nevertheless grow well with corn and beans, shading the soil and keeping it moist, according to a Garden Web forum on "Three Sisters With Sweet Potatoes."
But sweet potato is not rich in diosgenin (or dehydroepiandrosterone), a plant phyto-estrogen that interacts apparently with one of the hormones in estrogen, estradiol. Yam is, however.
Estradiol is produced by the adrenal glands and ovaries. It plays a role in the distribution of body fat in women. It peaks just before ovulation. The decline of this hormone in older women is associated with bone loss. In men it may prevent the apoptosis of sperm cells.
Blood Sugar and Digestion
The yam is also a bit better than sweet potato for lowering blood sugar. Both yams and taro root have been credited with aiding digestion, but this has not been backed up with research. The yam and taro root have quite long shelf lives (months and months), longer than those of sweet potatoes.
Complementing Amino Acids?
Beans, dairy foods, seafood, and meat or pork may complement the amino acids in these three tubers, providing the lysine needed to form connective tissue.
Yams, from the lily (or dioscoreaceae) family, have been cultivated for well over 8000 years in Africa and Asia. The word "yam" may come from the Wolof word "nyam" (the "n" is pronounced something like the "ng" sound in "ringing"), which means "taste," "eat," or "food," as well as "yam."
Other names for yam include "ete," which in Ewe, a Central West African language, "literally means swollen, according to oral history," says Maxwell Awuma of the Ghana News Agency. They are also called "agida," a Yoruba name for the tubers, "ube," the Phillipine name for purple yams, and "name" (in Publix supermarkets).
White yam (with brown skin and whitish flesh) is indigenous to Africa where it's a dietary staple; purple (or water) yam, a sweet yam with purple flesh, is indigenous to Asia. Other varieties may have other colors. One less-edible variety, the bulbifera, is invasive in Florida.
Yams take seven-to-ten months to mature. They are usually harvested in August or September. Although they like a warm moist climate, they tolerate drought. The tubers grow quite deep in the ground, and digging for these is apparently a feat.
The sweet potatoes belong to the morning glory family ("ipomoea batatas"). Indigenous to Central and South America (Peru), and perhaps the West Indies, they were originally called "camote," except by the Inca, who called them "batata." Hence the origin of the word "potato," says the Waine E. Bailey Produce Company ("A Brief History of the Sweet Potato"). Sweet potatoes have been cultivated for several thousand years. Columbus, Balbao, and Pizarro brought these to Spain and Africa, and from there sweet potatoes fmade their way to North America, becoming typical fare.
Sweet potato tubers are the easiest to grow of the three, apparently. They thrive in sandy soil, at various elevations, and again, in a warm moist climate. It takes no more than six months for them to reach maturity. The greens are harvested any time.
After being harvested however, sweet potatoes, have to be "cured," that is stored at room temperature for anywhere from one to three weeks (depending on the temperature), during which the starch in them is converted to sugar, so that they are sweet enough to bake well. Uncured they can be steamed, boiled, or fried. (Early season sweet potatoes may not be cured.)
Taro: Origin and Cultivation
The taro (also "kalo" and "cocoyam") is still another tropical vine with tuberous roots. It's a member of the araceae family, close to the lily, and like yam it's a dietary staple in the Pacific. Because of the huge leaves, taro plants may also be called "elephant ears" (or "yautia"), but it's not the same as the "elephant ears" that grow wild some places in the U.S., in Florida -- the latter are not good to eat. Taro can be grown in Florida too but requires more care than do wild elephant ears.
Taro grows in quite wet soil. Its roots can take up to a year to mature. The roots and tubers form quite near the surface, however, unlike the roots of the yam, and are easy to dig.
Yams, Hormones, and the Pill
Reportedly, yams have been used some in Africa as a natural "morning after pill," whether or not there is any research to back such use up. Also, West Africans, particularly the Yoruba, whose diet consists mostly of yams, have a high birth rate for twins. About 5% of Yoruba births are twins, which is perhaps ten times the expected rate, according to the AFP (2007).
In the 1940s, Mexican varieties of the yam (chosen over others because of their cheap-to-extract and abundant diosgenin,a type of phyto-estrogen) became the primary source of the steroid background used in most "steroidal" drugs, including progesterone, important in birth control pills and in treating menstrual disorders; and cortisone, important in treating arthritis.
Phyto-estrogens have a chemical structure which forms a basic "steroid background." Different chemical groups placed onto this background result in different steroids, including the sex hormones, according to Wayne's World.
Diosgenin as noted interacts perhaps with one of the hormones in estrogen. However, without further chemical processing, yam cannot replace natural progesterone (or other hormones), since the yam does not contain progesterone, of course, just a "backbone" for it.
Preparation: Sweet Potatoes
Sweet potatoes are steamed or fried, or, after curing, baked. They bake in just over an hour, depending on size. They can be started in a 425 degree oven and then after fifteen-to-thirty minutes, the temperature can be lowered to 375 degrees f., and the sweet potatoes cooked for another forty-five minutes to an hour or slightly more. When baked properly, the sweet potatoes become really sweet, like a candy almost.
Cooked sweet potatoes can be used in pies or casseroles, or even in a "yam cake" such as "Louisiana Yam Cake" (a spiced cake with sugar or brown sugar, flour, and mashed sweet potatoes, plus lots of eggs and some nuts). They hold together well and can be used instead of mashed potatoes to make a Southern (U.S.) favorite, potato biscuits. Breads and biscuits made with sweet potatoes tend to keep slightly longer than those made with regular potatoes.
Cooking is, as noted, even more important for yams than it is for sweet potatoes. The skins can be peeled before baking. Yams are richer in fiber and very moist and so take a bit longer to cook. Yams like sweet potatoes can be initially cooked at 425 degrees f. for a quarter or half an hour. Oven temperature can then be lowered to 400 degrees f., and baking continued for an hour or more.
If too large, the yams may need to be cubed to bake properly. However, outer flesh may brown and become tough during baking, and may have to be skinned before the yams are eaten or used in recipes. To avoid wasting too much flesh this way, yams should be cubed only after baking for at least forty minutes.
Traditionally, yams are boiled, peeled, and then mashed with palm oil to form a dough, or made into a soup. Alternately they are sliced and fried or (in Mexico) roasted and served with hot sauce and perhaps lime. They can also be lightly steamed, then dried and pounded into flour, called "elubo" (see a recipe for "Elubo" at Celtnet recipes).
Taro is prepared like yams, boiled or steamed and mashed into a dough or made into a soup, or alternately sliced and fried. Both taro and purple yams (which are the sweetest of yams) can also be baked into deep purple-colored sweet cakes, ice cream, or pudding.
Savory Latke, Au Gratin Yams and Sweet Potatoes, and More
Instead of potatoes, or along with them, shredded sweet potatoes, yams, and even taro can be used to make latke. And sliced yams or sweet potatoes, can be baked, perhaps together with potatoes, "au gratin." Another way to serve yams and sweet potatoes is to cube them and brush them with olive oil, and then roast them with herbs, peppers, and more. (Someday I'll try some roasted with hot chiles and peanuts.)
And root vegetables including yams or sweet potatoes or both, can be cubed, sauteed in oil and vinegar, and then stewed with some beans and/or peanuts (beans should be fairly tender when the sauteed vegetables are added). Yams or yam flour can be found in specialty shops and some health food stores.
Savory Yam Cake for an Abundant New Year?
Instead of a traditional New Year's savory cake "Lo bak gao," of shredded daikon radish, savory steamed cakes of either taro or yam can be prepared to celebrate the New Year, then sliced, fried, and eaten hot.
Since "gao," Chinese for "cake," is related to the word for "high," cakes may symbolize an increase or growth. Thus yam or taro cake might be served on the fifth day, for increased prosperity perhaps, as this is the day most businesses reopen after the New Year's holiday, or on the seventh, perhaps for growth and maybe even fertility (the seventh day is the day the goddess created humans and taught them about marriage so they could reproduce).
For more on Chinese New Year foods, see Erin de Santiago's "Chinese New Year Foods," or Grace Young's recipe for the cake, "Woo Tul Gow"). If you don't eat meat or at least not pork, you might try using sesame oil to fry the mushrooms and other ingredients in the cake, and find a substitute for the pork or bacon. Alternately, sweet cakes from purple yams, instead of savory cakes, might make nice festive deserts for other festivals.