Carbohydrate is the nutrient that provides the largest proportion of calories -- 45 to 65 percent -- in the American diet, as is recommended in the 2010 Dietary Guidelines for Americans.
This important nutrient used to be categorized as simple or complex, but the newest tools to evaluate the quality of carbohydrates are the glycemic index and glycemic load.
Glycemic Index
The glycemic index, or GI, was created in the 1980s by Dr. David Jenkins at the University of Toronto with the objective of helping people with diabetes better manage their blood sugar levels. To measure the GI of carbohydrate-containing foods, a serving providing 50 g of available carbohydrate is served to a minimum of ten participants. Their blood sugar levels are then measured over a period of two hours and compared to the glycemic response following the ingestion of pure glucose. The GI ranges between 0 and 100. Glucose has a GI of 100. A GI below 55 is considered low; between 56 and 69 is medium; and above 70 is high.
Glycemic Load
The glycemic index represents the quality of the carbohydrates in a food, but the glycemic load incorporates both the concept of quality and quantity to better estimate the impact of the consumption of carbohydrate-containing foods. The glycemic load, or GL, of a food is calculated by multiplying its GI by the amount of available carbohydrates in the serving to be eaten, divided by 100. The term "available carbohydrate" refers to the amount of digestible carbohydrates, which is the result obtained by subtracting the dietary fiber from the total carbohydrates. For example, a banana cake, with a GI of 47 and with 38 g of available carbohydrate per serving, has a GL of 18 and a large ripe banana, with a GI of 51 and 25 g of available carbohydrate, has a GL of 13. A GL below 10 is considered low; between 11 and 19 is medium; and above 20 is high.
Glycemic Load and Health
A number of large-scale and long-term studies have observed that the consumption of a high-GL diet constitutes an independent risk for developing type 2 diabetes or cardiovascular disease, as reported in the "American Journal of Clinical Nutrition." Therefore a lower dietary GL could have the benefit of helping you better manage your blood sugar and insulin levels in addition to helping you avoid suffering from the increasingly prevalent chronic diseases, such as coronary heart disease, type 2 diabetes and some common cancers.
Lowering Your Dietary Glycemic Load
The glycemic load is a complicated concept to use, especially since it does not appear on food labels. However, you can lower your GL and improve your health in two easy ways. Reducing your carbohydrate intake slightly and choosing more low-GI carbohydrates will help you decrease your dietary GL, which will benefit your health in the long-term. For example, instead of a large baked potato, have a small sweet potato; replace your serving of 2 cups of white pasta with 1 cup of whole grain pasta and add more vegetables to complete your meal; and select oat-based breakfast cereals without any added sugar instead of puffed rice cereals.
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
- Dietary Guidelines for Americans 2010: Carbohydrates
- "American Journal of Clinical Nutrition"; Glycemic index, glycemic load, and chronic disease risk---a metaanalysis of observational studies; Alan W. Barclay et al; 2008
