During the Holidays, I am reminded why sweet potatoes are my favorite winter vegetable. Sweet potatoes (Ipomoea batatas) are really not the potatoes at all. Potatoes are members of the Solanaceae family while sweet potatoes are members of the Convolvulaceae family - a family of plants that have trumpet-shaped flowers like the morning glory. Depending upon the sweet potato variety, of which there are about 400, its flesh may be either white, yellow or orange, and its thin skin may either be white, yellow, orange, red or purple. Sometimes this root vegetable will be shaped like a potato, being short and blocky with rounded ends, while other times it will be longer with tapered ends.

Sweet potatoes are grouped into two different categories depending upon the texture they have when cooked: some are firm, dry, and mealy, while others are soft and moist. In both types, the taste is starchy and sweet with different varieties having different unique tastes.

A Yam is Really a Sweet Potato

In the U.S., we tend to call the darker, sweeter sweet potato a yam. In actuality it is not a yam, rather it is in fact a variety of sweet potato. It was given the name yam after this variety of sweet potato was introduced into the United States in the mid-20th century in order to distinguish it from the white-fleshed sweet potato to which most people were accustomed. The name "yam" was adopted from "nyami", the African word for the root of the Dioscoreae family of plants which are considered true yams. The U.S. Department of Agriculture enforces mandatory labeling that the moist-fleshed, orange-colored sweet potatoes that are labeled as "yams" also be accompanied by the label "sweet potato."

If you ever eat a true yam, you will definitely know the difference. True yams have a very starchy and slippery texture and when cooked, will either be creamy or firm, depending upon the variety. Their taste is earthy and hardy, with most varieties having minimal, if any, sweetness.

History of the Sweet Potato

Sweet potatoes are native to Central America and are one of the oldest vegetables known to man. They have been consumed since prehistoric times as evidenced by sweet potato relics dating back 10,000 years that have been discovered in Peruvian caves.

Christopher Columbus brought sweet potatoes to Europe after his first voyage to the New World in 1492. By the 16th century, they were brought to the Philippines by Spanish explorers and to Africa, India, Indonesia and southern Asia by the Portuguese. Around this same time, sweet potatoes began to be cultivated in the southern United States, where they still remain a staple food in the traditional cuisine. In the mid-20th century, the orange-fleshed sweet potato was introduced to the United States and given the name "yam" to distinguish it from other sweet potatoes. Sweet potatoes are a featured food in many Asian and Latin American cultures. Today, the main commercial producers of sweet potatoes include China, Indonesia, Vietnam, Japan, India and Uganda.

Nutritional Highlights and Health Benefits

Clearly, the most important nutritional aspect of sweet potatoes is their excellent source of carotenes. In general, the darker the variety of sweet potato; the higher the concentration of carotenes. One cup of cooked sweet potatoes provides 30 mg of beta carotene. That translates to 50,000 IU pf vitamin A. It would take 23 cups of broccoli to provide the same amount. The redder variety of sweet potato is also an excellent source of lycopene. This red carotene has been shown to be extremely protective against the major cancers, i.e., breast, colon, lung, skin, and prostate cancer. It has been shown to lower the risk of heart disease, cataracts, and macular degeneration. Lycopene help prevents these diseases and others by neutralizing harmful oxygen free radicals before they can do damage to cellular structures.

Sweet potatoes are also a very good source of vitamin C and vitamin B6. In addition, sweet potatoes are a good source of manganese, copper, biotin, pantothenic acid, vitamin B2 and dietary fiber.

Sweet potatoes contain unique root storage proteins that have been shown to exert significant antioxidant effects. In one study, these proteins had about one-third the antioxidant activity of glutathione - one of the body's most important internally produced antioxidants.2 The presence of these proteins along with the high content of carotenes and vitamin C make sweet potatoes a valuable food for boosting antioxidant status.

Unlike many other starchy vegetables, sweet potatoes are classified as an "antidiabetic" food. Animal studies have shown that sweet potato helped stabilize blood sugar levels and improved the response to the hormone insulin.3 In this application, the white-skinned sweet potato (Ipomoea batatas) may be more beneficial. In a human study, consumption of this sweet potato consistently improved metabolic control in type 2 diabetic patients by decreasing insulin resistance.4

How to Select and Store

Use only high quality sweet potatoes that are firm and display the characteristic features of its variety. Remember the darker the variety, the higher the carotene content. Avoid wilted, leathery, or discolored sweet potatoes especially those with a green tint.

Sweet potatoes should be stored in a cool, dark and well-ventilated place, where they will keep fresh for up to ten days. They should be stored loose and not kept in a plastic bag. Keep them away from exposure to sunlight or temperatures above 60¡F since this will cause them to sprout or ferment. Uncooked sweet potatoes should not be kept in the refrigerator.

Tips for Preparing

If you purchase organically grown sweet potatoes, you can eat the entire tuber, flesh and skin. Yet, if you buy conventionally grown ones, you should peel them before eating since sometimes the skin is treated with dye or wax; if preparing the sweet potato whole, just peel it after cooking.

As the flesh of sweet potatoes will darken upon contact with the air, you should cook them immediately after peeling and/or cutting them. If this is not possible, to prevent oxidation, keep them in a bowl covered completely with water until you are ready to cook them.

Quick Serving Ideas

• Sweet potatoes are great on their own, they can be prepared in ways similar to Irish potatoes.
• Puree cooked sweet potatoes with bananas, maple syrup and cinnamon. Top with chopped walnuts.
• Thinly slice sweet potatoes, lightly coat with olive oil and your favorite seasonings. Bake the sweet potato chips in a medium-low (300¡F) oven until crispy.
• Spread mashed sweet potatoes on a piece of whole wheat bread, top with a layer of peanut butter and sliced apples.
• Steam cubed sweet potatoes, tofu, and broccoli. Mix in raisins and serve hot or cold with a curried vinagarette dressing.
• Desserts made with sweet potatoes are an autumn favorite but can be enjoyed year round. Try making sweet potato pie, bread, muffins or pudding.
• Baked sweet potatoes are delicious even when served cold and therefore make a great food to pack in to-go lunches.

Key references:

1. Weisburger JH. Lycopene and tomato products in health promotion. Exp Biol Med. 2002;227(10):924-7.
2. Hou WC, Chen YC, Chen HJ, et al. Antioxidant activities of trypsin inhibitor, a 33 KDa root storage protein of sweet potato (Ipomoea batatas (L.) Lam cv. Tainong 57). J Agric Food Chem 2001;49(6):2978-81.
3. Kusano S, Abe H. Antidiabetic activity of white skinned sweet potato (Ipomoea batatas L.) in obese Zucker fatty rats. Biol Pharm Bull 2000;23(1):23-6.
4. Ludvik B, Waldhausl W, Prager R, Kautzky-Willer A, Pacini G. Mode of action of ipomoea batatas (Caiapo) in type 2 diabetic patients. Metabolism 2003;52(7):875-80.

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Michael T. Murray, N.D., is widely regarded as one of world's leading authorities on natural medicine. A prolific author, Dr. Murray has written over 20 books on health and nutrition including the best-selling Encyclopedia of Natural Medicine and his latest book The Encyclopedia of Healing Foods. Dr. Murray is also Director of Product Development and Education for Natural Factors one of the leading manufacturers of natural products.