Whereas calculating the glycemic index requires human clinical trials, the glycemic load is a little simpler to determine. As long as you have some key pieces of information, you can calculate the glycemic load number and then see whether that number fits into the low, medium, or high category.
Doing the math
The glycemic load uses a specific calculation. So as long as you know the glycemic index of a food and the grams of available carbohydrates (total carbohydrate minus fiber) in that food, you can figure out that food's glycemic load. Here's the calculation:
Glycemic index x Grams of carbohydrates / 100
Try working out the calculation for a 1/2-cup serving of raw carrots, which have about 8.6 grams of available carbohydrates and a glycemic index of 45. (Note: Numbers are rounded for simplicity's sake. Feel free to do the same in your own calculations.)
45 x 8.6 = 387 / 100 = 3.9 glycemic load
Want to calculate the glycemic load of instant white rice instead? Well, a portion size of around 2/3 cup of white rice has about 36 grams of available carbohydrates and a glycemic index of 72. Here's the math:
72 x 36 = 2,592 / 100 = 26 glycemic load
To find the amount of available carbohydrates in packaged foods, simply check the nutrition facts label.
Figuring out what the numbers mean
Knowing how to calculate the glycemic load of a food is great, but it's not quite enough. The end measurement is what's most important to know. Similar to the glycemic index, the glycemic load is measured as low, medium, and high, rankings that help you determine your best choices for realistic portion sizes.
The measurements for glycemic load are as follows:
Low: 10 or less
Medium: 11 to 19
High: 20 or more
After you know the glycemic load of a food, think of these rankings and plop your food into place. You know that carrots have a glycemic load of 3.9. That's less than 10, so carrots have a low-glycemic load. White rice, with its glycemic load of 26, has a high glycemic load because 26 is greater than 20.
When you don't have time to calculate the glycemic load and match it up with the right measurement, keep in mind that foods with the least amount of carbohydrates (think vegetables and fruits) tend to have a lower-glycemic load than starchy foods (such as rice and pastas).
Factoring in portion sizes
Perhaps one of the greatest beauties of the glycemic load is that researchers have embraced it as the main standard of measurement, which means it's already calculated for you in most any glycemic index list. Three cheers for not having to drag a calculator with you everywhere you go!
The variable in this info, however, is portion size. If you're eating more or less than the portion size stated in the list you're looking at, you need to account for possible fluctuations in the glycemic load.
Consider the following different portion sizes of jasmine rice:
| Portion Size | Glycemic Load |
|---|---|
| 1/2 cup | 35 |
| 2/3 cup | 46 |
| 1 cup | 70 |
You can clearly see how the different portion sizes have a dramatic impact on the glycemic load. The higher the portion size, the greater the glycemic load will be. You can also see that, regardless of the calculation, the glycemic load for jasmine rice is so high that this food item isn't going to dip into the medium or low category very easily.
To see what happens in the case of a food that borders on being low-glycemic, take a look at brown rice, which has a glycemic index of 50:
| Portion Size | Glycemic Load |
|---|---|
| 1/2 cup | 12.5 |
| 2/3 cup | 16 |
| 1 cup | 26 |
The smaller portion size still doesn't bring the glycemic load of brown rice down to a low level, but it does keep it within the medium range. Increasing the portion size raises the glycemic load to the high level.
Last but not least, check out what happens to the glycemic load when you play with the portion size of a low-glycemic food such as kidney beans, which have a glycemic index of 34:
| Portion Size | Glycemic Load |
|---|---|
| 1/2 cup | 6 |
| 2/3 cup | 7 |
| 1 cup | 13 |
In this case, the two smaller portion sizes fall into a low-glycemic load, and the larger one moves into the medium range.
Just knowing the portion size will help you determine how much to eat. If the portion used is 2/3 cup and that food ends up being low-glycemic, you know you can easily eat that amount or less.
Of course, determining glycemic load based on portion size isn't an exact science, so sticking to low- to medium-glycemic foods within a reasonable amount is just fine. The beauty of this tactic for weight loss is that it keeps you eating portion sizes within a good calorie range.
Limiting your rice servings to 1/3 to 2/3 of a cup is a great place to be. If you increase that portion size to 1 to 2 cups, then you begin to not only increase your glycemic load but also your calorie intake.