• GL is measured in grams just like "net carbs" used in low carbohydrate products. Is it related?
• Yes. GL is a more accurate measure of the "net carbs" of a product which takes account of the different glycemic indices of the ingredients.
E.g. suppose we have a product of 3 carbohydrates. The glycemic load can be approximated by:
GL = GI 1 x [C1] + GI 2 x [C2] + GI 3 x [C3]
Where [C1] etc are the weights of carbohydrate of the different components. [ Ctot ] = [C1] + [C2] + [C3] is the total weight of carbohydrate. For the Low Carb market the crude assumption is made that each carbohydrate component is either totally glycemic (i.e. GI = 100%) or not glycemic at all (i.e. GI = 0). In the example above we assume C1 is glycemic carbohydrate and C2 and C3 not glycemic. For example, C2 and C3 could be fibre and polyols respectively. In this case:
GL = [C1]
i.e . GL = [ Ctot ] - [C2] - [C3]
So GL = "net carbs" = total carbs - fibre - polyols
This proves GL and "net carbs" attempt to measure the same thing.
• Of course we know that in a food product one ingredient can affect the GI of another so we can't really do this calculation like this and should measure GL directly and not calculate it.