Yam vs sweet potato: they are not the same thing, and they aren't even related. A sweet potato is the root of a plant in the morning glory family. A true yam is the tuber of a Dioscorea plant, related to lilies and grasses. Most "yams" sold in US supermarkets are really soft sweet potatoes with an old nickname.
If you grew up eating West African yam, you'll know the moment. There's an orange "yam" in an American supermarket, or a US recipe calling for one, and you think, that is not a yam. It isn't the tuber you pound or cook down into porridge.
Are yam and sweet potato the same?
No. The Library of Congress puts it plainly: yams and sweet potatoes are both flowering plants, but they aren't related botanically. Yams are monocots, plants that start with one seed leaf, from the Dioscoreaceae or yam family. Sweet potatoes are dicots, with two seed leaves, and belong to the Convolvulaceae, the morning glory family. Their Latin name is Ipomoea batatas.
One is closer kin to lilies, the other to morning glory, and they only look alike once they're peeled and boiled. That passing resemblance is the whole reason for the confusion.
Why most US "yams" are sweet potatoes
Sweet potatoes come in two broad types. "Firm" varieties stay firm when you cook them, while "soft" varieties turn soft and moist. In the United States the firm kind was grown first. When soft sweet potatoes started to be grown commercially, farmers and sellers needed a name to tell the two apart.
The name came from enslaved Africans, who had already been calling the soft sweet potatoes "yams" because they reminded them of the yams they knew from Africa. The word stuck to the soft varieties, and it's still on supermarket labels today. In the US, the USDA now requires any label saying "yam" to say "sweet potato" too.
So the "yams" in a lot of American recipes are sweet potatoes. Unless you go looking for yams, usually in an international market, you're probably eating sweet potatoes.
What is a real yam?
A real yam is the starchy tuber of a Dioscorea plant, native to Africa and Asia. There are over 600 varieties. Sizes run from a small potato to a tuber of 130 pounds (about 59 kg), the record as of 1999.
West Africa is where yam really lives. The International Institute of Tropical Agriculture (IITA) tracks where it grows. Its 2007 figures put Africa at 96% of world yam production, West Africa at 94% and Nigeria alone at 71%. The most important species in West and Central Africa is white Guinea yam, Dioscorea rotundata, which is native to West Africa, as is yellow yam, Dioscorea cayenensis. Water yam, Dioscorea alata, came from Asia and is now the most widely spread of them all.
In Nigeria yam gets pounded into iyan when the occasion matters, cooked down into porridge on a weekday and fried as dundun at the roadside. Among the Igbo, the New Yam Festival (Iri Ji) still marks the end of the farming season and the start of a new harvest. For more on what's inside a yam, see our guide to yam composition and nutrients.
Yam vs sweet potato nutrition
Here's how 100g of each compares once cooked, using figures from the USDA's FoodData Central database. The yam figures are for yam boiled or baked without salt, and the sweet potato figures are for sweet potato boiled without its skin.
| Per 100g, cooked | Yam | Sweet potato |
|---|---|---|
| Calories | 116 kcal | 76 kcal |
| Carbohydrate | 27.5g | 17.7g |
| Protein | 1.5g | 1.4g |
| Fibre | 3.9g | 2.5g |
| Fat | 0.1g | 0.1g |
| Water | 70.1g | 80.1g |
| Potassium | 670mg | 230mg |
| Vitamin A (RAE) | 6µg | 787µg |
| Vitamin C | 12.1mg | 12.8mg |
Gram for gram, cooked sweet potato has fewer calories and carbohydrates, because more of it is water. Yam has more fibre and nearly three times the potassium. Sweet potato's big lead is vitamin A, where the orange flesh puts it far ahead. Neither one wins outright, so pick the one your dish needs.
Yam vs sweet potato in the kitchen
Yams are starchier and drier than sweet potatoes, and the water figures above show it. Sweet potatoes, especially the soft orange ones sold as "yams" in the US, are moister and softer. Their skin can be white, yellow, red, purple or brown, and the flesh runs from white through yellow and orange to orange-red.
That difference matters once you start cooking. The dry, starchy body of white yam is what lets it pound into a smooth, stretchy dough for iyan. It's also what holds yam porridge together as it cooks down. Sweet potato is wetter, so it mashes soft but won't pound into a stretchy dough.
So if a recipe from Lagos or Accra says yam, a US supermarket "yam" won't give you the same dish. Head to an African or international grocer and ask for yam by name, or by the type: white yam, yellow yam or water yam.
AFN yam recipes to cook with real yam
Once you've got a proper tuber home, these are the AFN recipes to start with. For more yam dishes from across the continent, we've got a separate list.
Pounded yam (iyan)
White yam softened, then beaten until smooth, sticky and elastic. Our guide to the easy ways to make Nigerian pounded yam covers the mortar and pestle as well as the kitchen shortcuts. The Yoruba call it iyan, and it's what you serve when the occasion matters.
Asaro, Nigerian yam porridge
Yam cooked in a pepper and palm oil base until some of it collapses into a thick orange-red mash and some pieces stay whole. Asaro comes from the Yoruba of south-western Nigeria and is now eaten across the country.
Igbo yam porridge
The south-eastern version, seasoned with ogiri, crayfish and palm oil, with peppery uziza leaves stirred in at the very end. Our Igbo yam porridge is everyday food, eaten at breakfast or as a light lunch.
Yamarita
Yam strips dipped in a seasoned egg and flour coating, then fried until the crust is crisp and the inside stays soft. Yamarita is a modern Nigerian party favourite that sits on a small chops platter next to puff puff.
Mashed sweet potatoes
And if you've come home with sweet potatoes after all, cook them for what they are. Our mashed sweet potatoes go sweet with brown sugar and cinnamon, or savoury with garlic and herbs. There's more on them in our guide to sweet potatoes.
Yam and sweet potato questions
Are yams and sweet potatoes the same thing?
No. Yams belong to the yam family, Dioscoreaceae, and sweet potatoes to the morning glory family, Convolvulaceae. They aren't related, even though US shops often label soft sweet potatoes as yams.
Why are sweet potatoes called yams in the US?
Enslaved Africans called the soft sweet potatoes "yams" because they looked like African yams, and growers kept the name to tell soft varieties from firm ones. The USDA now requires a "yam" label to also say "sweet potato."
Can I use sweet potato instead of yam?
Not for West African yam dishes. Real yam is starchier and drier, which is what pounded yam and yam porridge depend on. Sweet potato is moister and softer, so the dish will come out differently.
Which is healthier, yam or sweet potato?
Neither wins outright. Per 100g cooked, sweet potato has fewer calories and far more vitamin A, while yam has more fibre and potassium.
Where can I buy real yams?
Usually at an African or international grocer rather than a mainstream supermarket. Ask for white yam, yellow yam or water yam.
Which country grows the most yam?
Nigeria. In IITA's 2007 figures it grew 71% of the world's yam, and West Africa as a whole about 94%.
