The bad rep: Potatoes rank high on the glycemic index, which measures how quickly different foods raise your blood sugar. Foods with a high GI value tend to cause a higher spike in blood sugar—and in insulin, the hormone that helps glucose get into cells—which can be a problem for some people, particularly those with diabetes.
The good news: Potatoes are a good source of fiber, potassium and vitamin C. And unless you’re eating an absolutely plain potato all by itself, its GI value doesn’t matter. (It’s also worth noting that the glycemic index is an imperfect and controversial scale.) A high-GI potato becomes a low-GI meal if you simply add a little olive oil, because the added fat helps slow the absorption of the potato’s carbohydrates.