Yams vs. Sweet Potatoes

A sweet potato is not a yam. A yam is not a sweet potato. A sweet potato is not a potato, nor is a yam. The US FDA, which regulates food labeling, does not have a standard of identity for either sweet potatoes or yams, so either term works. The US Department of Agriculture requires that labels with the word ‘yam’ on them also be accompanied by ‘sweet potato’.

They are both tuberous root vegetables that come from a flowering plant. The sweet potato is in the morning glory family, while yams are related to palms and grasses.
Yams are starchy and dry. Sweet potatoes are sweet and moist, some more than others.

Some yams and some sweet potatoes look similar. They are both tubers or edible roots.

Shape is the key. Sweet potato can be short and fat or long and thin, but it will always taper at the ends. Yams have a cylindrical shape with blackish or brown, bark-like skin and white, purple, or reddish flesh. Yams can be reddish or purplish as well, but most often, if you scrape the skin with a fingernail, you see white or cream-colored flesh. Most Americans have never had a real yam.

Sweet potatoes are grown in the United States, mainly North Carolina. Yams in Africa (where they originated), Southeast Asia, the Caribbean, and Central America.
Since the "soft" sweet potatoes slightly resembled true yams, they picked up the name and became labeled as "yams" in most US grocery stores. Common US Grocery Store Labeling
 Yam — Soft sweet potato with a copper skin and deep orange flesh.
 Sweet potato — Firm sweet potato with golden skin and lighter flesh.

A yam is super sweet and can grow over seven feet in length. Yams are toxic when eaten raw, but safe when cooked. A true yam is a starchy edible root of the Dioscorea genus. It is rough and scaly and very low in beta carotene.

Sweet Potato vs. White Potato Myth Debunked

The differences are much less than some experts would have us believe. These two tubers are very similar. The myth seems to stem from the fact that people tend to eat sweet potatoes baked or boiled, not fried, but more than a third of all white potatoes are consumed as either chips or French fries, so the sweet potato would appear to be less fattening by cooking style, not nutritional fact.

In a 100-gram portion, the white potato has 92 calories, 21 grams of carbs, 2.3 grams of fiber, 2.3 g of protein and 17% of the recommended daily value of vitamin C. White potatoes are higher in essential minerals, such as iron, magnesium, and potassium.

The same amount of sweet potato has 90 calories, 21 grams of carbs, 3 grams of fiber, 2 grams of protein, 35% of the recommended daily value of vitamin C and 380% of the daily recommended value of vitamin A.

Another difference is that sweet potatoes have a lower glycemic index than regular potatoes. The glycemic index is a measure of how quickly blood glucose levels rise after eating. Foods that have a low glycemic index do not cause a quick spike in blood sugar. As a result, people do not experience the same sugar highs and lows, which can lead to hunger and the consumption of extra calories. In other words, foods with lower glycemic indexes, like sweet potatoes and brown rice, make you feel full longer. However, baked white potatoes typically are eaten with cheese, sour cream, or butter. These toppings all contain fat, which also lowers the glycemic index of a meal.

Bottom line, the form in which you consume a potato, such as baked vs. fries is a more important difference than the type of potato.  Yams and sweet potatoes are not the same, but they are cousins and come from a different plant family.