A food's glycemic index (GI) is a measure of that food's effect on your blood sugar level. Diabetics who need to monitor their blood sugar should be aware of a food's GI before they eat it. A food with a GI of 0 has no carbohydrates at all. Glucose has the greatest effect on your blood sugar and therefore has a GI of 100. You can calculate the GI of a meal from the GI of the individual foods in that meal.
Step 1
Read the nutritional labels to get the amount of carbohydrates for each food in your meal. Assume that you're having a banana with 25 g of carbohydrates, shredded wheat with 37 g of carbohydrates and milk with 22 g of carbohydrates.
Step 2
Calculate the total amount of carbohydrates in the meal by adding the carbohydrates of each food together. This meal has a total of 25 + 37 + 22 = 84 g of carbohydrates.
Step 3
Compute the fraction of total carbohydrates in the meal that each food contributes. The banana has 25 g of carbohydrates and the total for the meal is 84 g of carbohydrates, so the banana provides 25/84 = 0.30 of the total. Similarly, the shredded wheat provides 37/84 = 0.44 of the total carbohydrates and the milk provides 22/84 = 0.26 of the total carbohydrates.
Step 4
Multiply the GI of each food by the fraction of carbohydrates provided by that food. Glycemicindex.com has an extensive database of GI values. For example, the banana has a GI of 58 and contributes 0.3 of the carbohydrates in the meal. The banana therefore provides a partial GI value of 58 x 0.3 = 17.4 for this meal. Shredded wheat has a GI of 63 and provides a partial GI value of 63 x 0.44 = 27.7. Milk has a GI of 32 and provides a partial GI value of 32 x 0.26 = 8.32.
Step 5
Add the partial GI values of each food to obtain the total GI for the meal. The partial GI value for the banana is 17.4, the partial GI value for the shredded wheat is 27.7, and the partial GI value for the milk is 8.32. The total GI value for this meal is therefore 17.4 + 27.7 + 8.32 = 53.4.
Things You'll Need
- Nutritional labels
- Calculator
- Glycemic index chart
