The question: What's the difference between yams and sweet potatoes? Is one healthier for you?

The answer: The terms yam and sweet potato are often used interchangeably in grocery stores. But they are two different starchy vegetables that deliver different nutrient profiles. In most cases, the "yams" sold in grocery stores are actually orange-coloured sweet potatoes.

The sweet potato is related to the morning glory family; it has orange flesh and its skin can be white, yellow, orange or purple. Sometimes it's shaped like a potato and sometimes it's longer and tapered at both ends.

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Yams belong to the lily family. The colour of their flesh varies from ivory to yellow to purple. They're long and cylindrical, and their skin has a rough and scaly texture. While sweet potatoes are readily available in grocery stores, yams aren't. If you're looking for yams and your grocery store doesn't carry them, try an international food market that carries Caribbean or African foods.

But when it comes to nutrition, sweet potatoes score much higher. Compared with yams, sweet potatoes are lower in calories and have far more beta-carotene (11.5 compared with 0.07 milligrams for each one-half cup), an antioxidant nutrient thought to guard against certain cancers.

There is no official recommended intake for beta-carotene but experts contend that consuming three to six milligrams daily will maintain blood levels in the range that's associated with a lower risk of chronic diseases. One-half cup of sweet potato supplies double that amount.

Sweet potatoes also have a lower glycemic index number than yams, meaning their carbohydrate is released more slowly into the bloodstream.

This doesn't mean yams aren't nutritious –they are a good source of fibre and potassium. Here's how sweet potatoes and yams compare nutritionally:

Sweet potato, 1/2 cup (100 grams), baked with skin:

90 calories, 0 grams fat, 20 grams carbohydrate, 3.3 grams fibre, 2 grams protein, 475 milligrams potassium, 20 milligrams vitamin C, 0.28 milligrams vitamin B6, 11.5 milligrams beta-carotene.

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Yam, 1/2 cup (100 grams), baked with skin:

116 calories, 0 grams fat, 27 grams carbohydrate, 4 grams fibre, 1.5 grams protein, 670 mg potassium, 12 milligrams vitamin C, 0.23 milligrams vitamin B6, .07 milligrams beta-carotene.

Send dietitian Leslie Beck your questions at dietitian@globeandmail.com . She will answer select questions, which could appear in The Globe and Mail and/or on the Globe website. Your name will not be published if your question is chosen.

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