Glycemic Load: What Is It?
Glycemic load (GL) represents an improvement over GI as a practical consumer aid in making smart food choices.
Like the glycemic index from which it is derived, glycemic load is also an indicator of carbohydrate "quality" (in terms of effect on blood sugar) of foods.
However unlike GI - which is a measure ONLY of the relative glycemic impact of different food types regardless of portion size - glycemic load ALSO takes into account the "total carbs" contained in a given portion size of any particular food type.
And therein lies its practical advantage over glycemic index.
For any serving size of a given food, the calculation of GL is simple:
Glycemic Load = GI x grams of carbohydrate / 100
The following example more clearly illustrates the difference between GI and GL in terms of every day utility. Suppose I'm choosing between a ripe banana and a ½" slice of watermelon for a snack.
What's my best choice? Which will have less glycemic impact (less disruption of my blood glucose levels)?
Just looking at the glycemic index of each (banana = 52; watermelon = 80) I would take the banana. That's easy, right? Well, actually…NO! If I check the glycemic load of these two choices, I would come to the opposite conclusion.
Because the slice of watermelon - being mostly water with only about half the carbohydrate content of the banana - has the lower glycemic load. This means that the slice of watermelon will have less glycemic impact than the banana!
Clearly then, the glycemic load is a far more useful and practical tool in guiding food choices than is the glycemic index.
Interpreting Glycemic Load Values
There is now fairly widespread agreement within the professional nutrition community that the following GL values represent the best guide to evaluating the actual glycemic impact of a specified amount of any given food:
- 0-10 = Low
- 11-19 = Intermediate
- 20 or more = High
Normally, as with our own low glycemic food lists, charts that list the GL of different foods specify a "portion size" used to derive the values expressed.
BEWARE: Virtually ANY food can be presented as having a low GL value if the portion size is small enough. GL values that do not specify a portion size are useless.
Glycemic load values remain the most practical metric of glycemic impact we have available today. As with the GI, glycemic load values are not precise measures and are best used to simply evaluate your dietary options as "good", "bad" or "intermediate". Applied in this manner, they can greatly simplify the lives of low glycemic dieters.
Nonetheless, it is clear that because such "calculated" GL values are derived directly from actual GI measurements, they also suffer from the same inherent problems pointed out in our discussion of the glycemic index; any errors in the GI will translate into error in the GL.
(Updated March 1, 2017.)