No, the two root vegetables are not really interchangeable.
If you’ve ever scanned the produce aisle for some sweet potatoes, spotted a sign for yams, and thought, “Well, they're basically the same thing... right?” you’re not alone. While they’re often marketed interchangeably (most likely because of a somewhat similar appearance), the truth is, yams and sweet potatoes are very different root vegetables.
According to Chef Marc Bauer, master chef at the International Culinary Center, a yam is characterized by dark and sometimes rough skin, though the flesh is whiter in shade and dry. “Yams require more oil, cream, or butter when cooked and are generally more starchy than the modern sweet potato,” Bauer says. They’re also grown all over the world. Roast them with other veggies for a delicious side dish, dice them up into a hearty yam stew, or, if you’ve got a sweet tooth, try a batch of candied yams coated in butter and brown sugar.
Sweet potatoes on the other hand, have a lighter skin, with tapered ends, and a light yellow to deep orange flesh. First introduced to the U.S. many decades ago, sweet potatoes have a naturally sweet taste (hence the name). As a result, you won’t have to add as much butter, oil, or cream in order to enjoy them, says Bauer. And when it comes to recipe ideas, the possibilities are endless: Try sweet potato fries, mashed sweet potatoes, roasted sweet potatoes, or loaded baked sweet potatoes (to name a few).
As for how they stack up nutritionally, both vegetables pack a big punch: According to Bauer, a 100-gram serving of yams provides about 30 percent of your daily dose of Vitamin C and about 800 mg of potassium. In contrast, the same 100-gram serving of sweet potatoes will give you more than three times the content of Vitamin A needed in your daily diet, with 330 mg of potassium. But if it’s calories you’re counting, sweet potatoes might be the way to go—they have more than 20 percent fewer calories than yams.