Sweet Potato vs Yam vs White Potato

 

Sweet potatoes (SchoolPhotoProject.com)

Sweet Potato or Yam?

Is it a sweet potato or yam? What many call a yam is actually a sweet potato (Ipomoea batatas). Although they may look and taste very similar, the true yam and sweet potato are not botanically related. Sweet potatoes belong to the morning glory family Convolvulaceae while yams belong to a different family called Dioscoreaceae. The edible parts of sweet potatoes are roots and in yams they are classified as tubers. Producing about 4-10 roots per plant, sweet potato plants yield more produce. There are typically 1-5 tubers per yam plant.

Sweet potatoes were grown in Peru as early as 750 BC. Native Americans were growing sweet potatoes when Columbus arrived in 1492. George Washington grew sweet potatoes on his farm at Mount Vernon, Virginia. Our sweet potatoes are “homegrown,” mainly in California, North Carolina, Mississippi, and Louisiana. Yams (Dioscorea spp.) are mainly grown in West Africa and Asia. Today the USDA requires that when the term 'yam' is used to describe sweet potatoes, it must also be labeled as a 'sweet potato'. Unless you specifically search for yams, which can often be found at ethnic markets, you are probably eating sweet potatoes.

Sweet potatoes are grown from sweet potato slips which are rooted sprouts from a mature sweet potato. Although seeds are available, yams are best grown from tubers purchased from a reputable dealer. White potatoes are grown from seed potatoes available online and at local nurseries.

Yams at a farmer's market (Eater.com)

According to Harvard University "Sweet potatoes with orange flesh are richest in beta-carotene. Sweet potatoes with purple flesh are richer in anthocyanins. Beta-carotene and anthocyanins are naturally occurring plant “phyto” chemicals that give vegetables their bright colors. These phytochemicals are being researched for their potential role in human health and disease prevention."

Univ. of North Carolina breeding sweet potatoes for people
in African countries. Photo: Courtesy U.N.C.

 And then there are white potatoes.

White potatoes (Solanum tuberosum) are the plant tubers while sweet potatoes are the plant roots. Harvard notes "If swapping sweet potatoes for white potatoes, you’ll still want to go easy on the portions: Though sweet potatoes are a rich source of beta carotene, they have a high glycemic index and glycemic load—almost as high as that of a white potato. Most people don’t eat sweet potatoes in the same over-sized quantities as they do white potatoes, which is perhaps why research studies haven’t found sweet potatoes to be a major culprit for weight gain and diabetes."
All these have good nutritional value and can be prepared many different ways. Sweet potatoes and yams are not just for the holidays. They make great soups, breads, and side dishes year-round.

Comparing nutrition value, according to the USDA, 1 cup cubed: Sweet potato: 130 calories, 3 grams of protein, 41 grams of carbohydrates, 3 grams of fiber, 16 grams of sugar. Yam: 155 calories, 2 grams of protein, 37 grams of carbohydrates, 5 grams of fiber, 0.7 grams of sugar. White potatoes: 116 calories, 3 grams of protein, 26 grams of carbohydrates, 3 grams of fiber, 1 gram of sugar.

CKagan, Master Gardener

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