SWEET POTATOES vs. YAMS

What's the difference between SWEET POTATOES and YAMS?

What is marketed in the United States as “yams” are actually a variety of sweet potato, grown in the South. A true yam is a starchy edible root of the Genus Dioscorea, and is generally imported to America from the Caribbean. It is rough and scaly and very low in beta carotene. “Yams,” as the industry and general public perceives them, are actually sweet potatoes with a vivid orange color and a soft moist consistency when cooked, and tend to have a sweeter flavor. Other varieties of sweet potatoes are lighter skinned and have a firmer, drier texture when cooked. Sweet potatoes are smooth with skins that can vary in color, depending on the variety, from pale yellow to deep purple to vivid orange. Flesh colors can range from light yellow to pink, red or orange.

Top: Yellow fleshed Yam, Boniato;
Bottom: Sweet Potato, White fleshed Yam.

So, where'd the confusion come?

Several decades ago when orange flesh sweet potatoes were introduced into the southern United States, producers and shippers desired to distinguish them from the more traditional white flesh types. The African word "nyami" referring to the starchy, edible root of the Dioscorea genus of plants was adopted in its English form, "yam". Yams in the United States are actually sweet potatoes with relatively moist texture and orange flesh. Although the terms are generally used interchangeably, the US Department of Agriculture requires that the label "yam" always be accompanied by "sweet potato."

Both are starchy, orange root vegetables with a natural sweetness, but according to Monica Reinagel on SELF.com, that's where the similarities end. You can check out NutritionData.com, where you can see that the sweet potato (which is related to the morning glory) is lower in calories, has a lower glycemic load, and is much higher in beta-carotene than the yam, which belongs to the lily family. The yam has higher levels of vitamin C and folate. The sweet potato does appear to be a better bet, nutritionally. But you probably don't need to worry about accidentally choosing the wrong vegetable for the Thanksgiving table.

A True Yam

True yams are larger than sweet potatoes--they can be up to the size of a man's arm. They're often cut into smaller chunks at the market.

Although Yams and Sweet Potatoes look and taste similar, Yams tend to be starchier and drier than a Sweet Potato. Both are flowering plants but that is where the similarites end; at least taxonomically. All flowering plants are split into two categories, monocot and dicot. Yams are a monocot and are closely related to lilys and grasses, and are native to Africa and Asia. Yams can vary in size from as little as the size of a small potato to record numbers of up to 130 pounds! Sweet Potatoes, on the other hand are a dicot and in the Morning Glory family. The skin color on Sweet Potatoes can vary in color from white, yellow, red, purple and even brown; the flesh colors also come in an array of colors ranging from yellow to orange to orange-red. There are firm and soft varieties of Sweet Potatoes. It is the soft variety of Sweet Potato that is often sold as a Yam in the US. More often than not you are eating Sweet Potatoes and not Yams, unless you purchased Yams at a ethnic market.

Nutritional Differences
So now that we have some background information on what separates the two tubers in the world of plants, lets look a little further into nutrition. Both Yams and Sweet Potatoes are both great health foods. But, they offer their own different nutritional benefits. Sweet Potatoes are well known for being packed full of nutrients and are still pretty low in calories. One Sweet Potato contains almost eight times the daily amount of Vitamin A recommended for adults, and significantly higher amounts of calcium, iron, vitamin E, and twice as much protein per serving as a Yam. Sweet potatoes contain less omega-3 fats than yams. The Yam and Sweet Potato are both loaded with potassium, magnesium, and phosphorous, as well as several so-called trace minerals: selenium, zinc, and copper. Whichever you choose, they are both great additions to the diet.

References:

- The Difference Between Sweet Potatoes and Yams? 

      by Monica Reinagel, MS, LD/N, November 17, 2010, on SELF.com 

- Yams vs. Sweet Potatoes; (10/19/2010), cooksfreshmarket.com

- Sweet Potato and Yam Differences

      by Peggy Trowbridge Filippone, About.com Guide 

- Sweet Potato; Wikipedia.com