Q. I keep reading that potatoes are high glycemic index and are therefore to be avoided. If you are eating, say, boiled potatoes with a meal that includes meat, doesn’t that retard the quick digestion of the potato and make it a valid part of a healthy meal?
A. Potatoes can have a high glycemic index (GI) - a measurement of how quickly a food raises blood sugar—and are linked to weight gain. But Katelyn Castro, a dietetic intern at Tufts' Frances Stern Nutrition Center, says, "The type of potatoes and preparation methods have a big impact on its glycemic response. Recent studies have found that waxy potatoes, like fingerling and red potatoes, have a lower glycemic index than starchy potatoes, like Russet and Idaho potatoes. The cooking method also alters the glycemic index of a potato. Boiled and roasted potatoes have the lowest GI (both 59), while baked potatoes are higher (69) and mashed and instant potatoes have the highest GI (78 and 82, respectively).
"Looking at the other foods eaten with the potato is also important, as you were thinking. One study found that when protein and fat are added to foods high in carbohydrates, this can lower the glycemic index of the food. Normally, foods high in carbohydrates, like potatoes, are quickly digested, broken down into glucose and released into the blood. When you add foods high in protein and fat, like meat or butter (GI = 0), this can slow digestion and slow the release of glucose into the blood. The study suggested that the protein and fat may trigger gut hormones and increase insulin secretion in order for this reduced glucose response to occur.
"While potatoes may have gotten a reputation of having a high glycemic index, by choosing specific types of potatoes, cooking methods and other additions to your meal, you can still enjoy potatoes in moderation without seeing spikes in your blood glucose levels."