Glycemic Index Help

Why do different Glycemic Indexes have different values for the same food?

Public Comments

1. This is because they are based on slightly differing scales. Look at the units used for temperature, for instance - they all do the same thing but use different numbers to express something. In the case of GI, this could be down to there being different units at more than one level - Glycaemic usually refers to glucose, but could be per gram or ounce or some other unit. In any event the numbers have to change if the reference material (glucose or other basic sugar) is altered.
2. The glycemic index is a measure of how *fast* a food you eat gets converted into glucose in your bloodstream. This measure depends on a number of factors - some constant and some variable. Some of the food factors affecting GI are carbohydrate content (starches and sugars), fiber content, the degree to which the food has been pre-processed, and how the food was prepared. The GI is measured by giving a fixed amount of a food to 10 human subjects and averaging the blood glucose response; so this could also contribute to variations in measurements. As the above poster mentioned, the GI value of a food is relative to a reference food - the reference food is given a value of 100 and the test food is given a value relative to that. I've heard of both glucose and white bread being used as the reference food. There may be others. So if the reference changes, then the test food GI value will change accordingly. I suspect another reason why different Glycemic Index Lists have different values for the same food, is because the values on each list probably originated from different testing labs. As mentioned above getting a precise GI measurement can be difficult - some lists state a range instead of a precise value. Most times the GI of a food is simplified by categorizing into a low (< = 55), medium (55 - 69), or high range (> 70). This makes knowing precise GI values less of an issue if your goal is simply to eat low GI foods. A more technical (and precise) explaination can be found at the American Journal of Clinical Nutrition: http://www.ajcn.org/cgi/content/full/76/1/5