Yams are tubers that are indigenous to West Africa, but they are commonly grown in the Southern United States and many South American countries. Yams are similar in appearance to sweet potatoes, white potatoes and rutabagas, but they are from a distinct plant lineage called the Dioscoreaceae family. Like all starchy root vegetables, yams contain carbohydrates but not quite as much as many other types, which makes them a good choice for diabetics or other people who want to control their blood sugar levels.
Yams are most frequently confused with sweet potatoes because they taste similar and have similar-colored flesh. Perhaps the best way to tell yams apart from other root vegetables is by their size. Yams grow to be much bigger than other root vegetables that are commonly available in U.S. grocery stores, which is why they are often sold precut and in packages. In contrast, sweet potatoes are significantly smaller and white potatoes are smaller still, which allows them to be conveniently sold from fresh produce displays. To give you a better idea of their size, yams typically grow to be at least 2 feet long and weigh more than 10 pounds. With favorable growing conditions, some yams weigh more than 30 pounds.
As a rule, root vegetables are high in starch, which is a type of carbohydrate that’s metabolized a little more slowly than carbohydrates found in baked goods and fruits. The end product of carbohydrate metabolism is a simple sugar called glucose, and starch takes more time to be reduced than other complex sugars. However, some starchy root vegetables have a much quicker impact on blood-glucose levels than others because they either contain more starch or the starch is metabolized a little quicker. For example, parsnips, white potatoes and sweet potatoes are very high in starch and consequently have high glycemic indexes because they raise blood-glucose levels relatively quickly and trigger a larger release of insulin from the pancreas. In contrast, yams have a much lower glycemic index, which means they are a much better choice for diabetics, who have trouble with high levels of blood glucose. The glycemic index of parsnip is 97, whereas for yams, it’s 37.
Carbohydrates and Other Nutrients
Yams are a good source of carbohydrates, as 1 cup of baked or broiled yams contains about 37 grams, which is 12 percent of the recommended daily amount for adults. That single cup of yams also contains about 5 grams of dietary fiber and various vitamins and minerals, especially vitamins C and B-6 as well as potassium, manganese and copper. Yams are very low in saturated fat, cholesterol and sodium, which are all linked to increased risk of cardiovascular diseases.
Dozens of varieties of yams exist, and some contain relatively high percentages of toxic alkaloids, so you should always cook them thoroughly to destroy the potentially harmful compounds. Bitter-tasting yams tend to have the most alkaloids. Yams are just as versatile as potatoes and can be cooked in a variety of ways including baked, broiled, grilled, fried, roasted, steamed, sautéed and microwaved. Yams go well with steak and are a nice addition to potato salad. They also work well in soups and stews.
- Encyclopedia of Human Nutrition; Benjamin Caballero et al.
- Contemporary Nutrition: Functional Approach; Gordon M. Wardlaw et al.
- The Nutribase Complete Book of Food Counts; Art Ulene
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.