The World's Healthiest Foods
Yam

Creamy or firm when cooked, yams have an earthy, hardy taste and usually a minimal amount of sweetness. Although they are available throughout the year their season runs from October through December when they are at their best.

There are approximately 200 different varieties of yams with flesh colors varying from white to ivory to yellow to purple while their thick skin comes in white, pink or brownish-black . Their shape is long and cylindrical (oftentimes having offshoots referred to as “toes”) while their exterior texture is rough and scaly. There is great confusion between yams and sweet potatoes in the United States; most of the vegetables labeled “yams” in the markets are really orange-colored sweet potatoes.

 


Health Benefits

Protection Against Cardiovascular Disease

Yams are a good source of vitamin B6. Vitamin B6 is needed by the body to break down a substance called homocysteine, which can directly damage blood vessel walls. Individuals who suffer a heart attack despite having normal or even low cholesterol levels are often found to have high levels of homocysteine. Since high homocysteine levels are signficantly associated with increased risk of heart attack and stroke, having a good supply of vitamin B6 on hand makes a great deal of sense. High intakes of vitamin B6 have also been shown to reduce the risk of heart disease.

Yams are a good source of potassium, a mineral that helps to control blood pressure. Since many people not only do not eat enough fruits and vegetables, but also consume high amounts of sodium as salt is frequently added to processed foods, they may be deficient in potassium. Low intake of potassium-rich foods, especially when coupled with a high intake of sodium, can lead to hypertension. In the Dietary Approaches to Stop Hypertension (DASH) study, one group ate servings of fruits and vegetables in place of snacks and sweets, and also ate low-fat dairy food. This diet delivered more potassium, magnesium and calcium. Another group ate a “usual” diet low in fruits and vegetables with a fat content like that found in the average American Diet. After eight weeks, the group that ate the enhanced diet lowered their blood pressure by an average of 5.5 points (systolic) over 3.0 points (diastolic). Dioscorin, a storage protein contained in yam, may also be of benefit to certain individuals with hypertension. Preliminary research suggests that dioscorin can inhibit angiotensin converting enzyme, which would therefore lead to increased kidney blood flow and reduced blood pressure.

Relief from PMS (Premenstrual Syndrome)and Menopausal Symptoms

Yams contain a unique fat-like substance called diosgenin. Diosgenin is technically classified as a hormone-like molecule and is currently being investigated experimentally for its potential anti-cancer effects. Contrary to some popular claims, the human body cannot convert diosgenin into the human hormone progesterone; however, yams are still a super food for women especially since they are a good source of vitamin B6.

One cup of baked cubed yam contains 24% of the daily value for B6, which is required by the liver (along with folic acid and other B vitamins) to detoxify estrogen by binding (conjugating) it to glucoronic acid, so it can be excreted from the body in the bile. This action is so beneficial that since the early 1970s, vitamin B6 has been successfully used in the management of many women’s cyclical conditions. At least a dozen double-blind, placebo-controlled trials have demonstrated positive effects of vitamin B6 in relieving PMS symptoms, including fibrocystic breast disease. Since recent research is showing that many of the negative symptoms associated with menopause, such as hot flashes, are also due to rapid rises in estrogen and/or excessively high estrogen levels, ensuring an adequate supply of vitamin B6 to help your body rid itself of extra estrogen is a smart idea.

Blood Sugar and Weight Control

Yams' complex carbohydrates and fiber deliver the goods gradually, slowing the rate at which their sugars are released and absorbed into the bloodstream. In addition, because they're rich in fiber, yams fill you up without filling out your hips and waistline. And one more benefit, yams are a good source of manganese, a trace mineral that helps with carbohydrate metabolism and is a cofactor in a number of enzymes important in energy production and antioxidant defenses. You've just got to hand it to Mother Nature; when She brings forth a food, She makes sure it integrates everything needed to contribute to your health and vitality.

Description

Yams are members of the Dioscoreae family. Depending upon the yam variety, of which there are about 200, its flesh may be of varying colors including white, ivory, yellow or purple while its thick skin may either be white, pink or brownish-black. Their shape is long and cylindrical (oftentimes having offshoots referred to as “toes”) while their exterior texture is rough and scaly. 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. Specific types of yams include Dioscorea alata (Hawaiian yam), Dioscorea batatas (korean yam) and Dioscorea esculenta (sweet yam).

Chances are this does not sound like the description of the “yams” that you had for Thanksgiving dinner. That is because most of the vegetables that are labeled “yams” in the United States are really orange-colored sweet potatoes. When the moist-fleshed orange-colored sweet potato was introduced into the United States in the mid-20th century, producers wanted to distinguish it from the white-fleshed sweet potato that most people were used to. They adopted the word “yam” from “nyami”, the African word for the root of the Dioscoreae genus of plants. While there are attempts to distinguish between the two, such as the U.S. Deparment of Agriculture's labeling requirement that the moist-fleshed, orange-colored sweet potatoes that are labeled as "yams" also be accompanied by the label "sweet potato", for many people this does not help to clarify the distinction between the two very different root vegetables. Yet, once you experience the distinct taste and texture of the real yam you will definitely know the difference, appreciating each of these root vegetables for their unique qualities.

History

Although it is uncertain from which country yams originated, yams are one of the oldest food plants known. They have been cultivated since 50,000 BC in Africa and Asia. In addition to these continents, yams also currently grow in the tropical and subtropical regions of North and South America.

Yams are one of the most popular and widely consumed foods in the world. They play a staple role in the diets of many different countries, notably those in South America, Africa, the Pacific Islands, and the West Indies.

How to Select and Store

How to Enjoy

For some of our favorite recipes, click Recipes.

A Few Quick Serving Ideas:

Purée cooked yam with a little milk and season with tamari, coriander, cumin and cayenne.

As yam has an earthy, deep taste, it nicely complements darker meats such as venison.

Add chunks of yams to your next stir fry or pan of roasted vegetables. Roasted yams, fennel, onions, and mushrooms are a delicious combination.

Safety

Yam is not a commonly allergenic food, is not included in the list of 20 foods that most frequently contain pesticide residues, and is also not known to contain goitrogens, oxalates, or purines.

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. For more detailed information on our Food and Recipe Rating System, please click here.

 

Yam, Dioscorea species, Cubes, Cooked
1.00 cup
157.76 calories
Nutrient Amount DV
(%)
Nutrient
Density
World's Healthiest
Foods Rating
vitamin C 16.46 mg 27.4 3.1 good
potassium 911.20 mg 26.0 3.0 good
manganese 0.50 mg 25.0 2.9 good
dietary fiber 5.30 g 21.2 2.4 good
vitamin B6 (pyridoxine) 0.31 mg 15.5 1.8 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

References

  • Ensminger AH, Ensminger, ME, Kondale JE, Robson JRK. Foods & Nutriton Encyclopedia. Pegus Press, Clovis, California.
  • Ensminger AH, Esminger M. K. J. e. al. Food for Health: A Nutrition Encyclopedia. Clovis, California: Pegus Press; 1986.
  • Fortin, Francois, Editorial Director. The Visual Foods Encyclopedia. Macmillan, New York.
  • Hsu FL, Lin YH, Lee MH et al. Both dioscorin, the tuber storage protein of yam (Dioscorea alata cv. Tainong No. 1), and its peptic hydrolysates exhibited angiotensin converting enzyme inhibitory activities. J Agric Food Chem 2002 Oct 9;50(21):6109-13.
  • Moalic S, Liagre B, Corbiere C, et al. A plant steroid, diosgenin, induces apoptosis, cell cycle arrest and COX activity in osteosarcoma cells. FEBS Lett 2001 Oct 12;506(3):225-30.
  • Wood, Rebecca. The Whole Foods Encyclopedia. New York, NY: Prentice-Hall Press; 1988.

This page was updated on: 2004-11-21 00:22:15
© 2002 The George Mateljan Foundation