According to a review done by A. Esfahani and associates in a 2009 issue of "The Journal of The American College of Nutrition," the glycemic index indicates the after-meal response your body has to a particular food compared to a standard amount of glucose. Many factors come into play in the assessment of the glycemic index, including the nature and amount of carbohydrates in the particular food, how refined or processed the food is, what the composition of the food is in terms of fiber, protein and fat and how the food was cooked.
Definition of the Glycemic Index
The glycemic index is determined by comparing the after-meal glycemic response of a food with the after-meal glycemic response to the same amount of available carbohydrate from a standard food in the same individual. The original standard was glucose, but later bread was used.
Generally, 50g or less of available carbohydrates from test and standard foods are tested by the same individual. The actual glycemic index value is the area under the blood glucose curve for the test food, expressed as a percentage of that of the standard control.
If glucose is used as the reference food, the value is multiplied by 100/70 for conversion to the bread scale. Generally, in accordance with the bread scale, low glycemic index foods are those that have a glycemic index value lower than 70, and high glycemic index foods are those with values over 100. Low glycemic index foods are those that elicit a low after-meal glucose response and include most fruits and vegetables and whole grain breads. High glycemic index foods are those that elicit a high after-meal glucose response and include, for instance, white bread, baked potatoes and white rice.
Definition of the Glycemic Load
The glycemic load examines the total impact of the dietary carbohydrate on your after-meal glycemia. The glycemic load is the product of the glycemic index of the food or diet under study and the grams of available carbohydrate in that food or diet divided by 100. For a meal, the glycemic load is calculated by multiplying the mean glycemic index weighted according to the grams of total available carbohydrates by the total grams in the meal or diet.
Health Implications
According to Esfahani's review in "The Journal of The American College of Nutrition," the available scientific evidence largely supports the notion that low glycemic index diets may have some value in the management and prevention of type 2 diabetes. The evidence, although not unanimous, also demonstrates a protective effect for low glycemic index diets against heart disease.
Limits of Glycemic Index and Glycemic Load
According to the Joslin Diabetes Center, affiliated with Harvard Medical School, health professionals agree that the more complex a meal plan is, the less likely you will follow it. The glycemic index is a fairly complex meal planning tool, and the fact that your blood glucose can react differently to so-called "low" and "high" glycemic index foods has limited the usefulness of the index in teaching patients with diabetes how to manage their food intake to keep their blood glucose under control. In a 2002 issue of the "American Journal of Clinical Nutrition" K. Foster-Powell and associates published an international table on glycemic index and glycemic load values that demonstrates the complexity of using the glycemic index.
Health professionals' preferences
According to the Joslin Diabetes Center, most dietitians and other health care professionals working with diabetic patients prefer to talk in terms of the number of grams of carbohydrate in a food, rather than the "glycemic index" of a food. Carbohydrates have the greatest effect on blood glucose, so in general two foods that have the same number of grams of carbohydrates in them will have a similar effect on your blood glucose level. A dietitian can work with you to determine, based on your weight, how active you are, and other factors, how many grams of carbohydrates you can eat at each meal and snack to keep your blood glucose under control, which is particularly essential for a diabetic patient. This type of meal planning is simpler to use, offers greater flexibility, and enables diabetic patients the ability to more successfully manage their condition.
References
- "Journal of the American College of Nutrition"; Glycemic Index: Physiological Significance; A. Esfahani, et al.; 2009
- "Journal of the American College of Nutrition"; Dietary Glycemic Index: Health Implications; J. Brand-Miller et al.; 2009
- Joslin Diabetes Center: The Glycemic Index and Diabetes
- "American Journal of Clinical Nutrition"; International table of glycemic index and glycemic load values: 2002; K. Foster-Powell et al.; 2002
