The Glycemic Index was created by comparing the blood sugar levels of volunteers after eating different foods. After an overnight fast, volunteers ate a quantity of food that provided 50 grams of energy-providing carbohydrates. Nutritionists took blood samples from the volunteers at 15- to 30-minute intervals over the next 2 hours to ascertain the volunteer's blood sugar and insulin response to the test food. Nutritionists compared the results with the response caused by consuming 50 grams of pure carbohydrate (usually glucose). Nutritionists then gave each food a number depending on how fast the body absorbed the carbs -- the high the number, the faster the absorption. The number is called the food's Glycemic Index or GI.

The Glycemic Index has three categories, and all foods fall into any one of the categories:

• GI of less than 55 = Low GI
• GI of 56-70 = Moderate GI
• GI of 71-100 = High GI