Ask The Expert
Eating Well

Just when you thought there was no such thing as a "free lunch," I'm happy to confirm that your understanding is partially correct.

It used to be that if there were more than 5 grams of fiber in the serving, then you would subtract the full amount of fiber grams from the grams of total carbohydrate. This is because dietary fiber is incompletely digested, absorbed, and metabolized. However, the rule has been modified now.

According to updated information from the Fall, 2008 issue of Diabetes Spectrum, as well as the updated ADA exchange list booklet called Choose Your Foods: Exchange Lists for Diabetes:  If the amount of fiber is greater than 5 grams per serving, then subtract half the grams of fiber from the total carbohydrate grams to determine the total adjusted carbohydrate grams.   So in the example you gave, if the total amount of carbohydrate per serving for that cereal were 18 grams, and if the fiber amount were 8 grams, then you would subtract ½ of the 8 grams of fiber, or 4 grams---meaning that 18 minus 4 = 14 grams for the adjusted amount of carbohydrate.  So you would use 14 grams as the carbohydrate count for that serving of cereal.