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The glycemic index (GI) can measure only how quickly one particular carbohydrate is converted into glucose in the body. It does not describe how much carbohydrate is in a certain food, or the influence on blood glucose levels of a variety of foods consumed in the typical single meal. Some foods have high-GI carbohydrate but do not have a great deal of it. It is important to know both how much carbohydrate is in a food and how quickly it converts into glucose.
The glycemic load (GL) calculates this information to more clearly determine the effect of food on blood glucose. The glycemic load of food is calculated using the following formula:
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Take the available amount of carbohydrates in a serving of food (total carbohydrates minus fiber).
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Multiply that number by the food’s GI.
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Divide by 100 for glycemic load.
For example, the GL of a half-cup serving of carrots would be calculated as:
8 (grams of carbohydrates) X 101 (GI) = 808 / 100 = 8.08, rounded to a GL of 8.
Based on these calculations, if people chose foods using only the glycemic index, they might avoid some nutritious items. The carrots have a higher GI than rice but have a lower GL. This comparison demonstrates that using glycemic load rather than just the glycemic index in choosing food provides more information. A lower glycemic load typically means less carbohydrates and more nutrients and fiber. In general, lower glycemic load foods provide a better diet.
Glycemic Index vs. Glycemic Load
Table of Common Single Foods
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Food (one serving)
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Carbohydrate Content (grams)
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Glycemic Index
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Glycemic Load
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Carrots
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8
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101
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8
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Lentils
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20
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41
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8
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White bread
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24
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100
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24
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Whole-grain bread
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24
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64
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15
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Baked potato
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37
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121
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45
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* lower than 131 according to some calculations
Ranges for GI and GL
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GI
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GL
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High
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70 or more
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20 or more
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Medium
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56 to 69
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11 to 19
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Low
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55 or less
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10 or less
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Foods with a low GL include high-fiber fruits and vegetables (other than potatoes), bran cereals, and many legumes (e.g., chick peas, kidney beans, black beans, pinto beans). Foods with a medium GL include pearled barley, brown rice, bulgur, rice cakes, whole grain pasta and fruit juices (unsweetened). Other high GL foods include French fries, refined cereal products, sugar-sweetened beverages, jelly beans, candy bars and white rice and pasta.
Calculating the GL is time-consuming and not always easy. It may be difficult to determine how many carbohydrates are in a serving of food. The GL does not take into account how the number changes during preparation and in combination with other nutrients, such as proteins and fats. This is another reason use of the glycemic index is viewed with caution when dealing with special diets (e.g., a diabetic diet) and why people on such diets should consult a registered dietitian.
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