The "Dietary Guidelines for Americans" recommends that Americans get between 45 percent and 65 percent of their calories from carbohydrates. However, not all carbohydrates have the same impact in your body and on your health. Carbohydrates used to be classified as being simple or complex according to the length of their molecule, but this classification is not appropriate to determine how carbohydrate-containing foods impact blood sugar levels and health. New tools, such as the glycemic index and the glycemic load, have been developed to better predict the response following the consumption of carbohydrates.
Glycemic Index
Dr. David Jenkins invented the glycemic index, or GI, in the 1980s to help diabetics better estimate the increase in their blood sugar levels after eating carbohydrate-containing foods. To measure the GI, the glycemic response during the two hours following the consumption of the equivalent of 50 g of available carbohydrate from a particular food is measured and compared against the glycemic response obtained after consuming pure glucose, which is attributed a score of 100. A GI value of 70 and above is considered high and represents foods that make blood sugar levels spike high, whereas a GI value of 55 and below is considered low and corresponds to foods that result in a smooth and small rise in blood sugar levels.
Glycemic Load
The glycemic load, or GL, was introduced in 1997 by researchers at Harvard University and is calculated by multiplying the available carbohydrate content of a food, in grams, by its GI value, divided by 100. The amount of available carbohydrate in a serving of food corresponds to the total carbohydrates minus the dietary fiber. For example, a large apple contains 25.1 g of carbohydrates and 4.4 g of fiber, which is the equivalent of 20.7 g of available carbohydrates. Because the GI of an apple is 38, a large apple will have a glycemic load corresponding to 7.9. A GL of 10 or less is considered low, between 11 and 19 is moderate, and above 20 is high.
Carbohydrate Quality Vs. Quantity
The main difference between the GI and the GL is that the GI measures the quality of the carbohydrates in a food, while the GL reflects both the quality and the quantity of carbohydrates contained in a serving of food. The GI, taken on its own, is a good tool to compare the potential impact of different carbohydrate-containing foods on your blood sugar levels. However, eating large servings of low GI foods can result in a significantly high dietary GL. Therefore, the GL concept is more complete than the GI alone.
GI and GL for Your Health
Consuming diets with a low GI and low GL have both been shown to be beneficial for your health. For example, a low dietary GI is associated with a healthier body weight, increased satiety and reduced cravings, improved athletic performance, increased insulin sensitivity, improved diabetes management and lower risk of cardiovascular disease, according to researchers at the University of Sydney. As for data concerning the GL, studies reported by the American Society for Clinical Nutrition show that long-term consumption of a high dietary GL is associated with an increased risk of developing coronary heart disease and type 2 diabetes.
References
- Harvard Health Publications: Carbohydrates and Health: Not that Simple...or that Complex
- University of Sydney: The Glycemic Index
- "American Journal of Clinical Nutrition"; International Table of Glycemic Index and Glycemic Load Value; Kaye Foster-Powell et al; 2002
- Harvard School of Public Health: Glycemic Index and Glycemic Load for 100+ Foods
- Dietary Guidelines for Americans 2010: Carbohydrates
