The glycemic index is the relative ranking of dietary carbohydrates based on their ability to raise blood glucose as compared to a reference carbohydrate. How you cook a food can change the potential of it to raise blood glucose levels by increasing or decreasing the availability of dietary carbohydrate to digestive enzymes and by adding or removing fat or indigestible carbohydrates, which can slow down carbohydrate digestion and absorption.
About the Glycemic Index
The GI is a tool that diabetics can use to manage their disease. The GI ranks foods based on a score according to how they raise blood sugar levels compared to pure glucose or refined white bread. Diabetics can pair high-GI foods with low-GI foods at the same meal to prevent extreme rise and fall in blood sugar. High-GI foods have a score greater than 75. Intermediate-GI foods have a score between 55 and 75. Low-GI foods have a score below 55.
Cooking Methods that Raise GI
Change in blood glucose levels following a meal is determined by the relative amount and availability of dietary carbohydrate to digestive enzymes, and the presence of dietary factors, such as fat or fiber, which slow down carbohydrate digestion. Any cooking method that breaks apart a grain or adds heat to a grain or carbohydrate will increase the glycemic index because it makes the dietary carbohydrates more available to digestive enzymes. For example, 1-one cup serving of instant mashed potatoes has a GI score of 88 compared to roasting a medium-sized baked potato, which has a GI score of 72.
Cooking Methods that Lower GI
Adding fat or fiber will slow down carbohydrate digestion and absorption, lowering the GI. For example, sauteing potatoes in olive oil versus boiling potatoes will lower the GI because it adds fat and is less destructive to the starchy potato carbohydrate. Slow-cooking carbohydrates by baking or steaming will result in a lower GI compared to boiling or microwaving. Leaving the skin on a potato versus peeling it will retain some of the indigestible fiber and lower the impact of the potato starch on blood glucose levels.
Considerations
Regardless of cooking method, some dietary carbohydrates, such as potatoes and refined grains, have a higher GI score than others. Choose whole grains, such as brown rice and whole-grain wheat bread, when possible, to control postprandial blood sugar levels. Furthermore, the GI of any food is based on your body's ability to digest and absorb carbohydrates. The exact scores and numbers vary among healthy subjects, people with diabetes and people with diabetes taking insulin. Talk to your dietitian if you need help planning meals for a diabetic diet.
