The short answer: Yams and sweet potatoes are completely different vegetables. No matter what you call them, in reality, most Americans are probably piling sweet potatoes onto their holiday dinner plates.
“The sweet potato is more Thanksgiving-ish,” said Chris Scott, chef at the Institute of Culinary Education. “There’s a wide range of things that you can do with them. You can make a sweet potato pie; you can roast them and serve [them] as-is or put any kind of topping on top.”
Yams, on the other hand, are much less common in the United States, Scott said. And it’s a safe bet that many Americans have never tried a true yam.
Somewhere along the way, the two terms became interchangeable. So what’s behind the sweet potato vs. yam confusion? We asked Scott and other food experts to explain.
The Difference Between A Sweet Potato And A Yam
Sweet potatoes and yams are both tuber vegetables, meaning they grow underground as a modification of a plant’s root or stem. Otherwise, they’re not closely related, said Alyssa Pike, manager of nutrition communications at the International Food Information Council Foundation.
Sweet potatoes likely originated in Central or South America, but the ones we eat most are U.S.-grown. Sweet potatoes also come in many different colors: purple, orange, yellow and brown on the outside, and white, yellow, orange and red on the inside, Pike explained. Sweet potatoes can also be white, but they are not related to regular white potatoes.
Yams originated in Africa, Asia and Central and South America, and come in hundreds of varieties. Yams are less common in the U.S. and usually imported, Pike said.
Scott said true yams more closely resemble yucca root, with skin that’s a fibrous, “tree-bark kind of texture.” Their flesh can be white, yellow, pink or purple.
Taste-wise, sweet potatoes tend to be sweet and moist, while yams are starchier and drier, with a milder flavor, he said.
How Sweet Potatoes And Yams Became Linked
The idea of calling a sweet potato a “yam” took hold around the 1930s, Scott said.
At that time, researchers at the Louisiana State University Horticulture Department decided to refer to the sweet potatoes grown in the state as “yams” in a national marketing campaign to distinguish Louisiana sweet potatoes, which farmers promoted as sweeter and moister with orange flesh, compared to the drier, lighter-fleshed versions grown in other parts of the country.
According to LSU, the name “yam” derives from the Senegalese term “nyami,” used by African slaves in the U.S. to describe sweet potatoes, which reminded them of the true yams native to Africa. The name was shortened to “yam,” and it stuck.
“In the U.S., the terms ‘yam’ and ‘sweet potato’ are often used interchangeably, but they both refer to what are technically sweet potatoes,” Pike said.
Some of the confusion is rooted in the fact that there are two main types of sweet potatoes grown in the U.S., each with different properties, and how they’re labeled in supermarkets, Pike said.
Soft sweet potatoes tend to be dark-skinned with orange flesh, and often labeled as “yams,” even though true yams are mostly found in specialty or international stores, Pike said. Firm sweet potatoes have golden skin and pale flesh and are most commonly labeled as sweet potatoes.
When using the term “yam” on labels for what are actually sweet potatoes, the U.S. Department of Agriculture also requires the label to include the phrase “sweet potato,” she said. For example, Bruce’s brand canned yams, founded in 1928 in Louisiana, include the description “cut sweet potatoes in syrup.”
“Although it may sometimes be called yams, it is more likely to be made from soft sweet potatoes with darker skin and orange flesh,” Pike said. “Confusing, I know.”
How To Cook Yams And Sweet Potatoes
True yams need to be boiled to break down the fibers and starches to “get rid of the woodiness,” Scott said. Cooking in liquid makes yams more palatable, and then they could be fried or braised.
Traditional orange-fleshed sweet potatoes can be prepared many ways, especially for Thanksgiving. Scott, who grew up in Coatesville, Pennsylvania, said his grandmother made sweet potato pie and “sweet potato fluff,” or mashed sweet potatoes topped with toasted marshmallows.
Now he likes to roast sweet potatoes with extra virgin olive oil and top with a mix of various seeds, like flax or sunflower, breadcrumbs, and nutritional yeast.
White sweet potatoes are usually drier than orange ones, and Scott said they work well roasted and made into a dumpling or gnocchi.
Which Is More Nutritious: A Yam Or A Sweet Potato?
The many different varieties of sweet potatoes and yams make generally defining their nutritional properties tough, said Michele Sidorenkov, a Phoenix-based registered dietician nutritionist and founder of My Millennial Kitchen.
Both contain carotenoids, a group of phytonutrients found in fruits and vegetables with red, orange or yellow pigments, she said. Carotenoids — shown to boost the immune system, guard against free radicals and decrease cancer risk — are more concentrated in produce with darker pigment.
Yams are higher in calories, carbohydrates, fiber and potassium, she said. Sweet potatoes are higher in sugar and may have more vitamin A and C, depending on the type.
“Deciding between a yam or a sweet potato as the healthiest option is really up to the individual and their health goals,” Sidorenkov said.
How the vegetables are prepared affects overall nutrition, she said. Adding extra salt and fat adds extra calories and sodium. Steaming, boiling or roasting sweet potatoes with little or no fat is the healthiest option.
Sweet potato skin is packed with nutrients, so Sidorenkov recommends not peeling them. Yams, however, have a tough skin and need to be peeled.
On holidays like Thanksgiving, celebrating food traditions and time with loved ones matters most, she said.
“Thanksgiving is not the time to be worrying about your diet or feeling guilty about enjoying the food on the table,” Sidorenkov said. “Thanksgiving is a time to connect with friends and family over food, stories and traditions.”
And, Scott said, if you still want to call your sweet potatoes yams, it’s really “not a big thing.”