Sweet potatoes

Although sweet potatoes may be part of the Thanksgiving tradition, be sure to add these wonderful naturally sweet vegetables to your meals throughout the year; they are some of the most nutritious vegetables around. Sweet potatoes can be found in your local markets year-round, however they are in season in November and December.

The sweet potato has yellow or orange flesh, 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. There is often much confusion between sweet potatoes and yams; the moist-fleshed, orange-colored root vegetable that is often called a "yam" is actually a sweet potato.

Health Benefits

How sweet it is for your health to eat sweet potatoes! Not only do they taste like dessert, here's the latest research on sweet potatoes surprising benefits.

Unique Proteins with Potent Antioxidant Effects

Sweet potato contain unique root storage proteins that have been observed to have significant antioxidant capacities. In one study, these proteins had about one-third the antioxidant activity of glutathione-one of the body's most impressive internally produced antioxidants. Although future studies are needed in this area, count on these root proteins to help explain sweet potatoes' healing properties.

A Sweet Source of Good Nutrition

Our food ranking system also showed sweet potato to be a strong performer in terms of traditional nutrients. This root vegetable qualified as an excellent source of vitamin A (in the form of beta-carotene), a very good source of vitamin C and manganese, and a good source of copper, dietary fiber, vitamin B6, potassium and iron. How do these sweet potato nutrients support our health?

An Antioxidant-Rich, Anti-Inflammatory Food

Since these nutrients are also anti-inflammatory, they can be helpful in reducing the severity of conditions where inflammation plays a role, such as asthma, osteoarthritis, and rheumatoid arthritis.

In addition, sweet potatoes are a good source of vitamin B6, which is needed to convert homocysteine, an interim product created during an important chemical process in cells called methylation, into other benign molecules. Since high homocysteine levels are associated with an increased risk of heart attack and stroke, having a little extra vitamin B6 on hand is a good idea.

If you or someone you love is a smoker, or if you are frequently exposed to secondhand smoke, then making vitamin A-rich foods, such as sweet potatoes, part of your healthy way of eating, may save your life, suggests research conducted at Kansas State University.

While studying the relationship between vitamin A, lung inflammation, and emphysema, Richard Baybutt, associate professor of nutrition at Kansas State, made a surprising discovery: a common carcinogen in cigarette smoke, benzo(a)pyrene, induces vitamin A deficiency.

Baybutt's earlier research had shown that laboratory animals fed a vitamin A-deficient diet developed emphysema. His latest animal studies indicate that not only does the benzo(a)pyrene in cigarette smoke cause vitamin A deficiency, but that a diet rich in vitamin A can help counter this effect, thus greatly reducing emphysema.

Baybutt believes vitamin A's protective effects may help explain why some smokers do not develop emphysema. "There are a lot of people who live to be 90 years old and are smokers," he said. "Why? Probably because of their diet…The implications are that those who start smoking at an early age are more likely to become vitamin A deficient and develop complications associated with cancer and emphysema. And if they have a poor diet, forget it." If you or someone you love smokes, or if your work necessitates exposure to second hand smoke, protect yourself by making sure at least one of the World's Healthiest Foods that are rich in vitamin A, such as sweet potatoes, is a daily part of your healthy way of eating.

So, the next time you have the urge for something sweet, how about a thick slice of sweet potato pie? It's one dessert guaranteed to satisfy your whole body, not just your sweet tooth.

Description

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.

The moist-fleshed, orange-colored root vegetable that is often thought of as a "yam" is actually a sweet potato. It was given this name 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 genus of plants that are considered true yams [http://www.whfoods.com/genpage.php?tname=foodspice&dbid=113]. While there are attempts to distinguish between the two, such as the mandatory labeling by the U.S. Department of Agriculture that the moist-fleshed, orange-colored sweet potatoes that are labeled as "yams" also be accompanied by the label "sweet potato," when most people hear the term "yam" they usually think of the orange-colored sweet potato as opposed to the true yam, the traditional Dioscoreae family root vegetable.

Sweet potatoes belong to the Convolvulaceae plant family and are known by the scientific name of Ipomoea batatas.

History

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.

How to Select and Store

Choose sweet potatoes that are firm and do not have any cracks, bruises or soft spots. Avoid those that are displayed in the refrigerated section of the produce department since cold temperature negatively alters their taste.

Sweet potatoes should be stored in a cool, dark and well-ventilated place, where they will keep fresh for up to ten days. Ideally, they should be kept out of the refrigerator in a cool, dry, dark place not above 60?F, which would fit the characteristics of a root cellar. Yet since most people don't have root cellars, we'd suggest just keeping your sweet potatoes loose (not in a plastic bag) and storing them in a cool, dark, and well-ventilated cupboard away from sources of excess heat (like the stove).

How to Enjoy

For some of our favorite recipes, click Recipes. [http://www.whfoods.com/recipestoc.php]

Tips for Preparing Sweet Potatoes:

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.

A Few Quick Serving Ideas:

Purée cooked sweet potatoes with bananas, maple syrup and cinnamon. Top with chopped walnuts.

Steam cubed sweet potatoes, tofu, and broccoli. Mix in raisins and serve hot or cold with a curried vinaigrette 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.

Safety

Sweet Potatoes and Oxalates

Sweet potatoes are among a small number of foods that contain measurable amounts of oxalates, naturally-occurring substances found in plants, animals, and human beings. When oxalates become too concentrated in body fluids, they can crystallize and cause health problems. For this reason, individuals with already existing and untreated kidney or gallbladder problems may want to avoid eating sweet potatoes. Laboratory studies have shown that oxalates may also interfere with absorption of calcium from the body. Yet, in every peer-reviewed research study we've seen, the ability of oxalates to lower calcium absorption is relatively small and definitely does not outweigh the ability of oxalate-containing foods to contribute calcium to the meal plan. If your digestive tract is healthy, and you do a good job of chewing and relaxing while you enjoy your meals, you will get significant benefits - including absorption of calcium - from calcium-rich foods plant foods that also contain oxalic acid. Ordinarily, a healthcare practitioner would not discourage a person focused on ensuring that they are meeting their calcium requirements from eating these nutrient-rich foods because of their oxalate content. For more on this subject, please see "Can you tell me what oxalates are and in which foods they can be found?" [http://www.whfoods.com/genpage.php?tname=george&dbid=48]

Nutritional Profile    Introduction to Food Rating System Chart

The following chart shows the nutrients for which this food is either an excellent, very good or good source. Next to the nutrient name you will find the following information: the amount of the nutrient that is included in the noted serving of this food; the %Daily Value (DV) that that amount represents (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and, the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. Read detailed information on our Food and Recipe Rating System.

References

Baybutt RC, Hu L, Molteni A. Vitamin A deficiency injures lung and liver parenchyma and impairs function of rat type II pneumocytes. J Nutr. 2000 May;130(5):1159-65. PMID:10801913.

Ensminger AH, Ensminger, ME, Kondale JE, Robson JRK. Foods & Nutriton Encyclopedia. Pegus Press, Clovis, California 1983.

Ensminger AH, Esminger M. K. J. e. al. Food for Health: A Nutrition Encyclopedia. Clovis, California: Pegus Press; 1986. PMID:15210.

Fortin, Francois, Editorial Director. The Visual Foods Encyclopedia. Macmillan, New York 1996.

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 Jun;49(6):2978-81. PMID:13860.

Li T, Molteni A, Latkovich P, Castellani W, Baybutt RC. Vitamin A depletion induced by cigarette smoke is associated with the development of emphysema in rats. J Nutr. 2003 Aug;133(8):2629-34. PMID:12888649.

Suzuki K, Ito Y, Nakamura S et al. Relationship between serum carotenoids and hyperglycemia: a population- based cross-sectional study. J Epidemiol 2002 Sep;12(5):357-66 2002.

Terahara N, Konczak-Islam I, Nakatani M, et al. Anthocyanins in callus induced from purple storage root of Ipomoea batatas L. Phytochemistry 2000 Aug;54(8):919-22. PMID:13870.

Wallerstein C. New sweet potato could help combat blindness in Africa. BMJ 2000 Sep 30;321(7264):786. PMID:13850.

Wood, Rebecca. The Whole Foods Encyclopedia. New York, NY: Prentice-Hall Press; 1988. PMID:15220.

Ylonen K, Alfthan G, Groop, L et al. Dietary intakes and plasma concentrations of carotenoids and tocopherols in relation to glucose metabolism in subjects at high risk of type 2 diabetes: the Botnia Dietary Study. Am J Clin Nutr. 2003 Jun; 77(6):1434-41 2003.

Recipes [http://www.whfoods.com/recipestoc.php]

Oxalates [http://www.whfoods.com/genpage.php?tname=george&dbid=48]

Vitamin A [http://www.whfoods.com/genpage.php?tname=nutrient&dbid=106]

Vitamin B6 [http://www.whfoods.com/genpage.php?tname=nutrient&dbid=108]

vitamin C [http://www.whfoods.com/genpage.php?tname=nutrient&dbid=109]