While it may not look like one, a banana is technically a berry, according to Purdue University. These fruits are a good source of fiber, potassium and vitamin C. Like any other carbohydrate-containing food, they can cause your blood sugar levels to increase. However, they aren't likely to cause blood sugar levels to spike as long as you watch your portion size.
A carbohydrate serving for a diabetic is 12 to 15 grams of carbs. This is the about the amount of carbohydrates in half of a medium banana. Out of the 27 grams of carbs in a medium banana, 3.1 come from fiber, which isn't broken down into glucose like other types of carbohydrates. Fiber helps slow the emptying of the stomach and thus keeps blood glucose levels from rising sharply.
The glycemic index measures how quickly a food causes your blood sugar to rise after you eat it. Foods with a GI score of 55 and under are considered low on the glycemic index, and unlikely to cause blood sugar spikes when consumed in moderation. Foods with a GI score of 70 or over are considered high on the glycemic index and are more likely to cause blood sugar spikes. The average GI score for bananas is 52, making them low on the glycemic index.
Increase in Blood Sugar
Each gram of carbohydrates you consume increases your blood sugar levels about the same amount depending on how much you weigh. In a 150-pound person this is about 4 milligrams per deciliter, and in a 200-pound person this is about 3 milligrams per deciliter, according to the University of Maryland Medical Center. So if you eat a whole medium banana and you weigh 150 pounds, your blood glucose levels will increase by about 108 milligrams per deciliter. However, given the relatively low GI score of bananas, this is likely to be a gradual increase rather than a sharp spike, which makes it easier for your body to deal with the increase and less likely your blood sugar levels will be above the 180 milligrams per deciliter the American Diabetes Association recommends one hour after eating.
Avoiding Blood Sugar Spikes
Spacing your carbohydrate and caloric intake evenly throughout the day will help minimize blood sugar spikes, so don't eat bananas at meals where you are eating a large number of carbs from other foods. Eat bananas at the same time as foods that contain high amounts of fiber or foods containing protein or healthy unsaturated fat to slow down digestion and the release of glucose into your bloodstream.
Based in Massachusetts, Jessica Bruso has been writing since 2008. She holds a master of science degree in food policy and applied nutrition and a bachelor of arts degree in international relations, both from Tufts University.