Most of the time we don’t eat servings of individual carbohydrate-type foods: we eat meals with a variety of foods containing varying amounts of carbs, as well as protein, fat and fiber. Thus in practice, for optimum blood-glucose management, we need to know the glycemic value of a meal, rather than simply the GI of individual foods.

How to Measure the Glycemic Index Value of Meals

To calculate the GI value of a meal, you need to know two things:

– The total grams of carbohydrates in the meal.
– The percentage of the carb-total contributed by each food.

Once you know this data, which is typically obtainable from most food composition or nutrition tables, the GI calculation for a meal is simple:

Multiply the GI value of each food by their percentage of total carbohydrate. Add up the totals, to get the GI value for the meal.

Calculating GI For a Simple Meal

  • Suppose you eat 2 slices (2oz) of toast and a glass (4oz) of milk.
  • The toast contains about 26g of carbohydrate; milk about 6g of carbs.
  • The total carb content is 32g. (81% from bread; 19% from milk)
  • The GI of bread is about 70; the GI of milk is about 28.

Calculation = GI X Percentage of carb contribution

Toast: 70 X 81% = 57
Milk: 28 X 19% = 5
Total: 57 + 5 = 62

The GI value of the meal is 62.

Calculating GI Value of Meals Not Always Possible

If we eat meals with non-standard foods that either do not have a GI rating, or are cooked in ways that have not been tested for GI effect, it is not possible to calculate a precise GI value for them. Even so, by using food composition tables and GI rating lists, it is possible to arrive at ballpark GI values for most meals.

GI Values of Meal
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