The diet of the Okinawans, a Japanese tribe known for their exceptionally long life expectancy, has been analyzed by many researchers and, according to the August 2009 issue of the "Journal of the American College of Nutrition," their diet is characterized by a low glycemic load, or low GL. In addition, a meta-analysis published in 2008 in the "American Journal of Clinical Nutrition" concluded that low GL diets are associated with a decreased prevalence of chronic diseases like cancer, type 2 diabetes and heart disease. Lowering the GL of your diet is a good way to improve your health, but it is important to first understand what it is exactly.
Available Carbohydrate Content
The first step to measure the glycemic load of a food is to determine its carbohydrate content per serving. Only carbohydrate-containing foods can have a glycemic index (GI) or glycemic load (GL). Because meat, chicken, fish, eggs, cheese, most nuts, avocado and non-starchy vegetables have a very low carbohydrate content, it is impossible to establish a GL for these foods. For all other foods, their available carbohydrate content can be obtained by subtracting the grams of dietary fiber from the grams of total carbohydrates in a typical serving. For example, a large apple with its skin contains 30.8 g carbohydrates and 5.4 g dietary fiber, which corresponds to 25.4 g available carbohydrates -- or 30.8 g minus 5.4 g.
Glycemic Index
The second step to calculate the GL of a food is to determine its GI. The GI of a food reflects the rate at which the carbohydrates are converted to sugar and absorbed into the bloodstream. To measure it, subjects are fed 50 g of available carbohydrates from a food and their blood sugar levels are measured during the following two hours. These results are compared against the results obtained with 50 g of glucose. For example, because the increase in blood sugar levels following the ingestion of an apple corresponds to 38 percent of the response observed after ingesting glucose, the GI of an apple is 38. The GI values of foods can be found in the "International table of glycemic index and glycemic load values" published in 2002 in the "American Journal of Clinical Nutrition."
Glycemic Load
The glycemic load of a food can be calculated by multiplying its available carbohydrate content, in gram, by its GI, divided by 100, as explained in the 2002 issue of the "American Journal of Clinical Nutrition." (See Reference 3) For example, a large apple, with an available carbohydrate content of 25.4 g and a GI of 38, has a GL of 9.7 -- 25.4 multiplied by 38, divided by 100. According to the Harvard School of Public Health, a GL of 10 and under is low, a GL between 11 and 19 is medium, and a GL of 20 and higher is high. (See Reference 5)
Low Glycemic Load Diet
A low GL can offer many health benefits, which can be obtained by controlling the two factors used in the calculation of the GL. The first way is to lower your carbohydrate intake and the second way is to choose foods with a lower GI. A combination of both ways is probably the best approach to reduce your dietary glycemic load. For example, you can decrease your carbohydrate intake by eliminating refined grains and foods containing added sugar from your diet and you can choose low GI carbs, such as brown basmati rice, quinoa, barley or whole grain pasta, over high GI options, such as potatoes or white rice.
References
- "Journal of the American College of Nutrition"; The Okinawan diet: health implications of a low-calorie, nutrient-dense, antioxidant-rich dietary pattern low in glycemic load; Willcox D.C., et al.; August 2009
- "American Journal of Clinical Nutrition"; Glycemic index, glycemic load, and chronic disease risk---a metaanalysis of observational studies; Alan W. Barclay, et al,; 2008
- "American Journal of Clinical Nutrition"; International Table of Glycemic Index and Glycemic Load Value; Kaye Foster-Powell, et al.; 2002
- University of Sydney: The Glycemic Index
- Harvard School of Public Health: Carbohydrates and the Glycemic Load
