Carbohydrates have a glycemic index, which is essentially the impact a particular serving of food has on the glucose level of a person's blood. Each food is ranked as either low, medium or high. This ranking is ultimately due to the rate in which the food breaks down in the body. Something that breaks down rather fast will generally release much more sugar into the blood in a fairly short amount of time than food having a more gradual rate of digestion.
Things You'll Need
- Glycemic chart
Add together the total number of carbohydrate grams within a given meal. Let's use a breakfast of toast, cereal and milk for this example--43 g of carbohydrates in shredded wheat, 13 g of carbohydrates in milk and 17 g in a slice of white bread. This gives us a total of 73 g of carbohydrates.
Divide the grams of carbohydrate in a piece of food by the total carbohydrate in the meal. This will give you the percentage of carbohydrates a piece of accounts for within the meal. The shredded wheat would account for 59 percent, the bread would account for 23 percent and the milk would account for 18 percent.
Multiply the various percentages of the foods, in this case the shredded wheat, the bread and the milk, by their glycemic index (see Resources). Shredded wheat has an index of 63, giving it an index within the meal of 37.17. Milk has an index of 32, giving it an index within the meal of 5.76. White bread has an index of 70, giving in an index within the meal of 16.1.
Add each figure together to get the glycemic index of the meal, which would be 59.03 for the meal described.