Glycemic Index and Glycemic Load

    The carbohydrates in different foods have differently strong capabilities to raise the blood sugar; the glycemic index of food z is defined as: blood sugar increase by x gram carbohydrates in y gram food z GI(z)= —————————————————————————————————————————————————————————————— ·100 blood sugar increase by x gram Glucose The GI characterizes the activity of the carbohydrates in food z, but is more useful if one knows how much y gram of the food provides those x gram carbohydrates. The glycemic load incorporates this relationship: blood sugar increase by y gram food z GL(z)= —————————————————————————————————————— ·100 blood sugar increase by y gram Glucose The numerators of GI and GL are really the same. Further, since - blood sugar increase by x gram Glucose   carbohydrate weight x —————————————————————————————————————— = —————————————————————— blood sugar increase by y gram Glucose       total weight y we have x GL(z)=GI(z)·— y where x/y is only a function of the type of food z (namely its relative carbohydrate content).
    However, a different definition of GL is also used where the serving size y is different from the glucose reference size Y':
blood sugar increase by y gram food z GL'(z)= ——————————————————————————————————————— ·100 blood sugar increase by Y' gram Glucose Now we have the relationship blood sugar increase by x gram Glucose    carbohydrate weight x ——————————————————————————————————————— = —————————————————————— blood sugar increase by Y' gram Glucose       weight Y' which leads to x GL'(y,z)=GI(z)·—— Y' where Y' is always selected to be 100 gram.
    Whereas GL describes the blood sugar increase by food z of any serving size relative to glucose of the same serving size, GL' relates the blood sugar increase of a particular serving size (y, with carbohydrate content x) to 100g of glucose. This latter definition gives distorted GL-values for any serving sizes except 100 g. For example, glucose has a GL=100; but 10g of glucose have a GL'=10, which sounds misleadingly innocuous. People may remember the GL'-value ("the good news") but forget the serving size ("the bad news") while they are eating.
    On the internet is a report by the University of Sidney, Australia, with a long table of the GI and GL values of many foods. Its abstract and introduction defines GL twice according to the formula above, but the actual table lists GL' values, as stated in a footnote. Their serving sizes are arbitrary and vary widely. In contrast, the table provided here constitutes an excerpt with foods that are at least somewhat meaningful to Americans and GL numbers valid for any serving size, recalculated according to
100 GL=GL'·——— y