The glycemic index (GI) is a measure of the effect that a particular food has on your blood sugar level. This value ranges from 0 to 100, such that a food with no carbohydrates has a GI of 0 and pure glucose has a GI of 100. Diabetics must be concerned about the GI of their meals in order to manage their blood sugar level. You can calculate the GI of an entire meal from the amount of carbohydrates in each food and the GI of each food in the meal.
Step 1
Read the nutritional label for each food in your meal. This provides the number of grams of carbohydrates in a serving. Assume for this example that your meal consists of shredded wheat with milk and toast. The milk contains 23g carbohydrates, the shredded wheat 43g carbohydrates and the toast 28g carbohydrates.
Step 2
Calculate the total amount of carbohydrates in your meal. The milk has 23g, the shredded wheat 43g and the toast 28g. The total carbohydrate load in the meal is 23 + 43 + 28 = 94g.
Step 3
Compute the fraction of the total carbohydrate load that each food in the meal provides. The meal has a total of 94g carbohydrates and the milk 23g carbohydrates, so the milk provides 23/94 = 0.245 of the carbohydrates in the meal. Similarly, the shredded wheat provides 43/94 = 0.457 of the carbohydrates in the meal. The toast provides 28/94 = .298 of the carbohydrates in the meal.
Step 4
Multiply the fraction of the carbohydrate load of each food by that food's GI. You can get the GI values for various foods from the GI database at Glycemicindex.com. Milk has a GI of 32, so its contribution to the GI of the meal is 32 x 0.245 = 7.8. Shredded wheat has a GI of 63, so its contribution to the GI of the meal is 63 x 0.457 = 28.8. Toast has a GI of 70, so its contribution to the GI of the meal is 70 x 0.298 = 20.9.
Step 5
Calculate the total GI for the meal by adding the GI contribution from each food. The milk contributes 7.8, the shredded wheat 28.8 and the toast 20.9. The total GI for the meal is therefore 7.8 + 28.8 + 20.9 = 57.5.
Things You'll Need
- Nutritional labels
- Calculator
- Glycemic index chart
