The development of the glycemic index in 1981 changed the way nutritionists and the world viewed carbohydrates. Once classified as either simple or complex, carbohydrates serve as the main source of energy for the body. Because complex carbohydrates, including starchy foods like potatoes and bread, consist of a more complex structure, scientists believed it took the body longer to break them down, making them the more desirable carbohydrates to consume. The fact that the body does not respond to all carbohydrates the same led to the creation of the glycemic index and, later, the glycemic load.
Glycemic Index
All carbohydrates consist of sugar molecules. The body breaks down these sugar molecules and converts them to glucose -- the type of sugar, also known as blood sugar, that cells use for energy. The glycemic index ranks carbohydrates based on how rapidly they cause blood sugar to increase. The glycemic index scale ranges from 0 to 100. To determine the glycemic index of each food, scientists measure and plot the blood sugar response to 50 g of that particular carbohydrate as a curve and compare the area under the curve to a control food like pure glucose.
High vs. Low
The glycemic index scale provides information on what foods have a high GI and what foods have a low GI. Foods with a GI of 70 or higher, like white bread, processed cereals, white rice and potatoes, are considered high glycemic index foods. Doctors consider those foods with a GI between 56 and 69, like rye bread and bananas, as medium GI foods. Foods are considered low GI foods if they contain a GI of 55 or less.
Glycemic Load
The glycemic index was initially created as a tool to help those with diabetes better control their blood sugar. Now many weight loss programs use the glycemic index. The thinking behind it is that eating only foods with a low GI will promote weight loss because those foods take longer to break down, therefore providing a feeling of fullness longer and reducing the number of calories consumed. The glycemic index alone, however, does not take into account how much of a certain food you eat. You can convert the glycemic index into the glycemic load, which takes into account both the GI and the amount consumed, so it describes both the quality and quantity of carbohydrate.
Calculation
To determine the glycemic load, multiply the GI of the carbohydrate by the amount of carbohydrate consumed, in g, and then divide the product by 100. For example, white bread has a GI of 76. If you consume 1 slice, it contains 14 g of carbohydrate. Multiply 76 times 14 and then divide by 100 to get the glycemic load per serving of 10.64. In contrast, rye bread with a GI of 41 and 12 g of carbohydrates provides a glycemic load of 4.92. You can track your dietary glycemic load by adding the glycemic load for each food you consume in your diet.
