Written by Mary Jane Brown, PhD, RD (UK) on September 21, 2017 Source: Health line Photos Source: Health line
The terms “sweet potato” and “yam” are often used interchangeably, causing a lot of confusion.
While both are underground tuber vegetables, they are actually very different.
They belong to different plant families and are only distantly related.
So why all the confusion? This article explains the key differences between sweet potatoes and yams.
What Are Sweet Potatoes?
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Sweet potatoes, also known by the scientific name Ipomoea batatas, are starchy root vegetables.
They are thought to originate in Central or South America, but North Carolina is currently the largest producer (1Trusted Source).
Surprisingly, sweet potatoes are only remotely related to potatoes.
Like a regular potato, the tuberous roots of the sweet potato plant are eaten as a vegetable. Their leaves and shoots are also sometimes eaten as greens.
However, sweet potatoes are a very distinctive-looking tuber.
They are long and tapered with a smooth skin that can vary in color, ranging from yellow, orange, red, brown or purple to beige. Depending on the type, the flesh can range from white to orange to even purple.
There are two main types of sweet potatoes:
Dark-Skinned, Orange-Fleshed Sweet Potatoes
Compared to golden-skinned sweet potatoes, these are softer and sweeter with a darker, copper-brown skin and bright orange flesh. They tend to be fluffy and moist and are commonly found in the US.
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Golden-Skinned, Pale-Fleshed Sweet Potatoes
This version is firmer with a golden skin and light yellow flesh. It tends to have a drier texture and is less sweet than dark-skinned sweet potatoes.
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Regardless of the type, sweet potatoes are generally sweeter and moister than regular potatoes.
They are an extremely robust vegetable. Their long shelf life allows them to be sold year-round. If stored correctly in a cool, dry place, they can keep for up to 2–3 months.
You can buy them in a wide range of different forms, most often whole or sometimes pre-peeled, cooked and sold in cans or frozen.
Summary: Sweet potatoes are a starchy root vegetable originating in Central or South America. There are two main varieties. They have a long shelf life and are usually sweeter and moister than regular potatoes.
What Are Yams?
Yams are also a tuber vegetable.
Their scientific name is Dioscorea, and they originate in Africa and Asia. They are now commonly found in the Caribbean and Latin America as well. Over 600 varieties of yams are known, and 95% of these are still grown in Africa.
Compared to sweet potatoes, yams can grow very large. Size can vary from that of a small potato to up to 5 feet (1.5 meters). Not to mention, they can weigh up to an impressive 132 pounds (60 kgs) (2Trusted Source).
Yams have some distinct characteristics that help distinguish them from sweet potatoes, mainly their size and skin.
They are cylindrical in shape with brown, rough, bark-like skin that is difficult to peel, but it softens after heating. The flesh color varies from white or yellow to purple or pink in mature yams.
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Yams have a unique taste, too. Compared to sweet potatoes, yams are less sweet and much more starchy and dry.
They also tend to have a good shelf life. However, certain varieties store better than others.
In the US, true yams can be tough to find. They are imported and rarely found in local grocery stores. Your best chances of finding them are in international or ethnic food stores.
Summary: True yams are an edible tuber originating in Africa and Asia. There are over 600 varieties, which vary widely in size. They are starchier and drier than sweet potatoes and rarely found in local grocery stores.
Why Do People Confuse Them?
So much confusion surrounds the terms sweet potatoes and yams.
Both names are used interchangeably and often mislabeled in supermarkets.
Yet, they are completely different vegetables.
A few reasons can explain how this mix-up happened.
Enslaved Africans brought to the US called the local sweet potato “nyami,” which translates to “yam” in English. This is because it reminded them of true yams, a food staple they knew in Africa.
In addition, the darker-skinned, orange-fleshed sweet potato variety was only introduced to the US several decades ago. In order to set it apart from paler-skinned sweet potatoes, producers labeled them “yams.”
The term “yam” is now more of a marketing term for producers to distinguish between the two types of sweet potatoes.
Most vegetables labeled as a “yam” in US supermarkets are actually just a variety of sweet potato.
Summary: Confusion between sweet potatoes and yams arose when US producers began using the African term “nyami,” which translates to “yam,” to distinguish between different varieties of sweet potatoes.
They Are Prepared and Eaten Differently
Both sweet potatoes and yams are very versatile. They can be prepared by boiling, steaming, roasting or frying.
The sweet potato is more commonly found in US supermarkets, so as you’d expect, it is used in a wider range of traditional Western dishes, both sweet and savory.
It is most often baked, mashed or roasted. It is commonly used to make sweet potato fries, an alternative to baked or mashed potatoes. It can also be puréed and used in soups and desserts.
As a staple on the Thanksgiving table, it’s most often served as a sweet potato casserole with marshmallows or sugar or made into a sweet potato pie.
On the other hand, true yams are rarely found in Western supermarkets. However, they are a staple food in other countries, particularly those in Africa.
Their long shelf life allows them to be a steady food source during times of poor harvest (3Trusted Source).
In Africa, they are most often boiled, roasted or fried. Purple yams are more commonly found in Japan, Indonesia, Vietnam and the Philippines and often used in desserts.
Yams can be bought in a number of forms, including whole, powder or flour and as a supplement.
Yam flour is available in the West from grocers specializing in African products. It can be used to make a dough that is served as a side with stews or casseroles. It can also be used similarly to instant mashed potatoes.
Wild yam powder can be found in some health food and supplement stores under various names. These include wild Mexican yam, colic root or Chinese yam.
Summary: Both sweet potatoes and yams are boiled, roasted or fried. Sweet potatoes are used to make fries, pies, soups and casseroles. Yams are more commonly found in the West as a powder or health supplement.
Their Nutrient Content Varies
A raw sweet potato contains water (77%), carbohydrates (20.1%), protein (1.6%), fiber (3%) and almost no fat (4).
In comparison, a raw yam contains water (70%), carbohydrates (24%), protein (1.5%), fiber (4%) and almost no fat (5).
A 3.5-ounce (100-gram) serving of baked sweet potato with the skin on contains (4):
Calories: 90
Carbohydrates: 20.7 grams
Dietary fiber: 3.3 grams
Fat: 0.2 grams
Protein: 2 grams
Vitamin A: 384% DV
Vitamin C: 33% DV
Vitamin B1 (Thiamine): 7% DV
Vitamin B2 (Riboflavin): 6% DV
Vitamin B3 (Niacin): 7% DV
Vitamin B5 (Pantothenic acid): 9% DV
Vitamin B6 (Pyridoxine): 14% DV
Iron: 4% DV
Magnesium: 7% DV
Phosphorus: 5% DV
Potassium: 14% DV
Copper: 8% DV
Manganese: 25% DV
A 3.5-ounce (100-gram) serving of boiled or baked yam contains (5):
Calories: 116
Carbohydrates: 27.5 grams
Dietary fiber: 3.9 grams
Fat: 0.1 grams
Protein: 1.5 grams
Vitamin A: 2% DV
Vitamin C: 20% DV
Vitamin B1 (Thiamine): 6% DV
Vitamin B2 (Riboflavin): 2% DV
Vitamin B3 (Niacin): 3% DV
Vitamin B5 (Pantothenic acid): 3% DV
Vitamin B6 (Pyridoxine): 11% DV
Iron: 3% DV
Magnesium: 5% DV
Phosphorus: 5% DV
Potassium: 19% DV
Copper: 8% DV
Manganese: 19% DV
Sweet potatoes tend to have slightly fewer calories per serving than yams. They also contain a bit more vitamin C and more than triple the amount of beta-carotene, which converts to vitamin A in the body.
In fact, one 3.5-ounce (100-gram) serving of sweet potato will supply you with almost all of your daily recommended amount of vitamin A, which is important for normal vision and the immune system (4).
On the other hand, raw yams are slightly richer in potassium and manganese. These nutrients are important for good bone health, proper functioning of the heart, growth and metabolism (6Trusted Source, 7Trusted Source).
Both sweet potatoes and yams have decent amounts of other micronutrients, such as B vitamins, which are vital for many bodily functions, including producing energy and creating DNA.
It is also important to consider the glycemic index (GI) of each. The GI of a food gives an idea of how slowly or quickly it impacts your blood sugar levels.
GI is measured on a scale of 0–100. A food has a low GI if it causes blood sugars to rise slowly, whereas a high GI food causes blood sugars to rise quickly.
Cooking and preparation methods can cause a food’s GI to vary. For example, sweet potatoes have a medium-to-high GI, varying from 44–96, whereas yams have a low-to-high GI, ranging from 35–77 (8).
Boiling, rather than baking, frying or roasting, is linked to a lower GI (9Trusted Source).
Summary: Sweet potatoes are lower in calories and higher in beta-carotene and vitamin C than yams. Yams have slightly more potassium and manganese. They both contain decent amounts of B vitamins.
Their Potential Health Benefits Are Different
Sweet potatoes are a great source of highly available beta-carotene, which has the ability to increase your vitamin A levels. This can be very important in developing countries where vitamin A deficiency is common (10Trusted Source).
Sweet potatoes are also rich in antioxidants, particularly carotenoids, which are thought to help protect against heart disease and decrease the risk of cancer (11Trusted Source, 12Trusted Source).
Certain types of sweet potatoes, especially purple varieties, are thought to be the highest in antioxidants — much higher than many other fruits and vegetables (13).
Also, some studies suggest that certain types of sweet potatoes can help improve blood sugar regulation and reduce “bad” LDL cholesterol in people with type 2 diabetes (14Trusted Source, 15Trusted Source, 16Trusted Source).
Meanwhile, the health benefits of yams have not been extensively studied.
There is limited evidence that yam extract may be a helpful remedy for some of the unpleasant symptoms of menopause.
One study in 22 postmenopausal women found that a high intake of yams over 30 days improved hormone levels, reduced LDL cholesterol and increased antioxidant levels (17Trusted Source).
It’s important to remember that this was a small study, and more evidence is needed to confirm these health benefits.
Summary: The high antioxidant content of sweet potatoes may protect against disease, as well as improve blood sugar regulation and reduce “bad” LDL cholesterol. Yams may help relieve symptoms of menopause.
Adverse Effects
Although sweet potatoes and yams are considered healthy and safe foods to consume for most people, it may be wise to follow certain precautions.
For example, sweet potatoes have fairly high levels of oxalates. These are naturally occurring substances that are usually harmless. However, when they accumulate in the body, they can cause problems for people at risk of kidney stones (18Trusted Source).
Precautions must also be taken when preparing yams.
While sweet potatoes can safely be eaten raw, certain types of yams are only safe to eat when cooked.
Naturally occurring plant proteins found in yams can be toxic and cause illness if consumed raw. Peeling and cooking yams thoroughly will remove any harmful substances (19Trusted Source).
Summary: Sweet potatoes contain oxalates that can increase the risk of kidney stones. Yams must be cooked thoroughly to remove naturally occurring toxic substances.
The Bottom Line
Sweet potatoes and yams are completely different vegetables.
However, they’re both nutritious, tasty and versatile additions to the diet.
Sweet potatoes tend to be more readily available and are nutritionally superior to yams — albeit only slightly. If you prefer a sweeter, fluffier and moister texture, opt for sweet potatoes.
Yams have a starchier, drier texture but might be harder to find.
You really can’t go wrong with either.
What did you learn about sweet potatoes and yam? Have you confused them in the past? Make sure to get yams for your pounded yams recipe? How can sweet potatoes and yams contribute to your diet?
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