A food's glycemic index, or GI, is a measure of how quickly the carbohydrates in that food enter your blood stream as blood glucose. The scale for the GI runs from 0 to 100. A food with no carbohydrates at all has a GI of zero, and pure glucose has a GI of 100. You may frequently need to calculate the GI for a meal to ensure it's below a certain value if you're diabetic.
Step 1
Use a GI database to determine the GI of each component in the meal. The University of Sydney maintains a GI database with many different foods. Assume for this example that the meal is shredded wheat with milk. Shredded wheat has a GI of 67 and milk has a GI of 34.
Step 2
Determine the grams of carbohydrates for each component in the meal. You can obtain this information from the nutritional label for each component. Assume for this example that the shredded wheat contains 22g of carbohydrates and the milk contains 13g of carbohydrates.
Step 3
Calculate the percentage of carbohydrates that each component contributes towards the meal. The shredded wheat has 22g of carbohydrates and the milk has 13g of carbohydrates, so the entire meal has 22 + 13 = 35g of carbohydrates. The shredded wheat therefore contributes 22 / 35 x 100 = 62.9 percent of the carbohydrates in the meal. The milk contributes 13 / 35 x 100 = 37.1 percent of the carbohydrates in the meal.
Step 4
Multiply each component's GI from Step 1 by that component's carbohydrate percentage from Step 3. This will provide each component's partial GI value of the meal. Shredded wheat has a GI of 67 and a carbohydrate percentage of 62.9, so the partial GI value of shredded wheat in this meal is 67 x 0.629 = 42.1. Milk has a GI of 34 and a carbohydrate percentage of 37.1, so the partial GI value of milk in this meal is 34 x 0.371 = 12.6.
Step 5
Add the partial GI values from step 4 together to obtain the total GI of the meal. The partial GI value of the shredded wheat is 42.1 and the partial value of the milk is 12.6. The total GI of the meal is therefore 42.1 + 12.6 = 54.7.
Things You'll Need
- Calculator
- Glycemic index chart
- Nutritional information chart
