How is Glycemic Index Calculated?

The Glycemic Index (GI) is a numerical scale used to rank carbohydrates based on their effect on blood sugar levels. It assesses how quickly a carbohydrate-containing food increases blood glucose compared to a reference food, typically glucose or white bread. The calculation involves comparing the blood sugar response to a standard amount of the test food with the response to the reference food.

The process for calculating the Glycemic Index is as follows:

1. Selection of Test Subjects:
   • Healthy individuals are chosen for the study.
   • Baseline fasting blood glucose levels are measured for participants.
2. Reference Food Consumption:
   • Participants consume a measured quantity of the reference food, a substance known to elevate blood sugar rapidly.
3. Blood Glucose Measurements:
   • Blood glucose levels are measured at various intervals after consuming the reference food.
   • The resulting response curve illustrates the speed at which blood sugar rises and falls.
4. Test Food Consumption:
   • Participants then ingest a measured amount of the test food containing the specific carbohydrate being studied.
5. Blood Glucose Measurements for Test Food:
   • Blood glucose levels are measured at the same intervals as after consuming the reference food.
6. Calculation of Glycemic Index:
   • The Glycemic Index is determined by comparing the area under the blood glucose response curve for the test food with that for the reference food.
   • The formula typically used is: GI = (Area under the curve for test food / Area under the curve for reference food) x 100.
7. Classification of GI:
   • Foods are then categorized based on their Glycemic Index value:
     • Low GI (55 or less)
     • Medium GI (56-69)
     • High GI (70 or more)

It’s essential to recognize that while the Glycemic Index is a valuable metric, other factors such as the Glycemic Load (GL), which considers both the quality and quantity of carbohydrates, may offer a more comprehensive understanding of a food’s impact on blood sugar.