The Glycemic Index, or GI, debuted in 1981. Its job is to describe how carbohydrates you eat or drink can affect your blood sugar. Ultimately, the goal is to help you make wise nutritional decisions. It isn't a perfect tool, and there's lots of information about your blood sugar response that the glycemic index doesn't tell you. However, the glycemic index is a helpful starting point and a teaching tool, especially for diabetics and those with other metabolic illnesses. The official database of GI food scores is maintained by the University of Sydney School of Molecular and Microbial Biosencence's Human Nutrition Unit.
Impact on Blood Sugar
The main purpose of the glycemic index is to score carbohydrate-containing foods on a scale of 0 to 100 according to how they affect your blood sugar, or glucose, after consumption. Blood sugar is created when you eat and is used to supply your body's cells with fuel. The score is indexed to a standard amount of glucose in a reference food.
Not All Carbs Are Created Equal
There are three main kinds of carbohydrates, differing mainly by their molecular makeup. The most basic unit of carbs is the simple sugar. These are found in fruits, milk, sweets like candy, syrups and desserts; and in white bread and products made with white flour. Fiber and starches are two kinds of complex carbohydrates. Starches are long chains of sugar molecules linked together, making storage of energy easy. Potatoes and rice are examples of starch. Fiber is the non-digestible form of a carbohydrate. Found in plant foods, fiber promotes regularity and a sense of fullness. Beans, peas, lentils and bran are great sources of fiber.
Choose the Healthier Option
All carbohydrates are fuel sources for the body, and as such, they fall somewhere on the glycemic index. Carbs are considered high-GI if they rank at 70 or higher, medium at 56 to 59 and low at 55 or less. Simple carbs generally have high GI scores, while complex carbs tend to be low-GI foods. High-GI foods are usually rapidly digested and cause a conspicuous fluctuation in your blood sugar levels. Low-GI foods, on the other hand digest more slowly, so their effect on blood sugar tends to be more gradual. The scientists behind the Glycemic Index say it helps you choose foods that are lower on the scale and, therefore, also helps reduce your risk of diabetes and heart disease and control your weight.
What the GI Doesn't Tell You
The Glycemic Index is often criticized for what it doesn't tell you. For example, Harvard's Joslin Diabetes Center says many factors come in to play in determining how your blood sugar will respond after you eat carbs. Your age, activity level, how much fiber and fat were in the food, whether it was a processed or whole food, how it was cooked and how quickly you generally digest food are important factors. Level of acidity and any substance you take to speed digestion are additional factors, says a Florida State University dietitian. MIT adds that the time you eat and how close it was to your last workout is yet another. And these factors vary from person to person, so a one-size-fits-all score could be misleading. Joslin says the tool is useful for teaching diabetics how to manage their food intake and keep their blood sugar controlled.
References
- University of Sydney: Home of the Glycemic Index
- American Diabetes Association: Glycemic Index and Diabetes
- Joslin Diabetes Center: The Glycemic Index and Diabetes
- Florida State University; The Glycemic Index; Sandra Woodruff
- MIT: Glycemic Index
- "American Journal of Clinical Nutrition"; International Table Of Glycemic Index and Glycemic Load Values: 2002; Kaye Foster-Powell et al.; July 2002
