Limitations of GI measurement

In the real world, we eat food in portion sizes. Each food type has its own “usual” portion.

Glycemic load (GL) is a more realistic measurement than Glycemic Index of the effect on our blood sugar levels of carbohydrate containing foods, since it takes into consideration the usual portion sizes of each food. (1, 2)

The calculation of GL is GL=GI/100 * Net carbohydrates. The result is given in rounded numbers (integers) and rated in the following way:

• Low GL = 10 or less
• Medium GL = 11-19
• High GL = 20 and above

Since the GL is measured using realistic portions rather than servings, it is calculated differently than nutrient content. Nutrient content uses the servings while GL uses the standard portions. If your portion is, for instance, two times higher than what is considered as standard, multiply the GL by 2.

For example, consider grapes:

The usual portion is considered to be 120g which contains 19g of carbohydrates.
GL = 9 which falls in the Low category.

If you eat double that amount – 240g at once seating, the GL = 18 (9*2). A GL of 18 falls in the Medium category.

What it means is that while eating 120g of grapes doesn’t have a big effect on your sugar spikes, eating 240g will.

Here is an example of how the GL of oranges depends on the amount of oranges consumed and how we consume them:

FoodGIPortion(g)Carbs (g)GLRank
Orange (medium)33120103Low
2 oranges (medium)33240206Low
Orange juice (glass)462502612Medium
Large orange juice465005224High 