The glycemic index is a scale that ranks different foods based on the rate at which the body digests and they enter the bloodstream. Foods with a high glycemic index enter the bloodstream very quickly and cause blood glucose levels to incur a sharp spike, followed by a sudden drop. Foods with a low glycemic index enter the bloodstream more slowly and cause a more subtle, but steady rise in blood glucose levels.
Glycemic Index Formula
To calculate the glycemic index of a food, nutritionists first give a portion of about 50 g of the food to a sample of 10 healthy individuals. They then draw blood from each at 15 to 30 minute intervals over the next two hours. These samples allow nutritionists to create a graph of each individual's blood-sugar response and calculate what is called the "area under the curve," or the sum of all individuals' responses combined. The AUC of the test food is then divided by that of a reference food with a similar glucose level, and multiplied by 100 to get a glycemic index.
Criticisms
The glycemic index of a particular food is not a constant number, as different sample populations will experience different blood glucose effects. Furthermore, the glycemic index simply measures a food's effect on blood glucose levels, but provides little information about that food's overall nutritional value. For example, sugar and candy have about the same glycemic index as many vegetables.
Glycemic Load
To address criticisms of the glycemic index, researchers developed the glycemic load -- a measure of the amount of available carbohydrates in a particular food based on its serving size. Glycemic load is calculated by multiplying a particular food's glycemic index by the amount of carbohydrates it contains, and then dividing this number by 100. The glycemic load provide a more accurate indication of various carbohydrates' nutritional value.
Diet Tips
A diet composed of foods that have a high glycemic load can lead to weight gain, diabetes and cardiovascular disease. Try to consume mostly foods with a glycemic load of less than 20. Sugar, white bread, potato products and canned and processed foods have high glycemic loads. Fresh fruit and vegetables, foods high in fiber and beans and legumes have low glycemic loads and can help you reduce your risk glycemic-related health problems.
