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
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.