The Truth about the Glycemic Load – Tells You How Much Carb (Sugar) Your Food Actually Contains (Whereas the Glycemic Index Only Measures the Effect of Glucose on Your Blood Sugar) The glycemic index on its own can be very helpful, but there were some people who felt that it had 1 serious limitation. While it measured how quickly the sugar of a particular food entered your bloodstream & spiked your glucose level, it didn’t take into account how much carb (sugar) was actually in that food.