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.
Glycemic load: 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: Multiply the glycemic index by grams of carbohydrates and divide by 100.
So 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 is 45 times 8.6, which equals 387; Divide that by 100 and you get a glycemic load of 3.9 — rounding the numbers for simplicity’s sake.
To find the amount of available carbohydrates in packaged foods, simply check the nutrition facts label. If the food is raw, like carrots or apples, use a glycemic index table, such as the one at Glycemic Index Foundatione.
Glycemic load: 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:
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.
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).
Glycemic load: 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. Check out some comparisons:
| Jasmine Rice | Brown Rice | Kidney Beans | |||
|---|---|---|---|---|---|
| Portion Size | Glycemic Load | Portion Size | Glycemic Load | Portion Size | Glycemic Load |
| 1/2 cup | 35 | 1/2 cup | 12.5 | 1/2 cup | 6 |
| 2/3 cup | 46 | 2/3 cup | 16 | 2/3 cup | 7 |
| 1 cup | 70 | 1 cup | 26 | 1 cup | 13 |
So jasmine rice is never going to be low-glycemic, but a small portion of brown rice is within the medium range. And even a cup of kidney beans carries just a medium glycemic load; smaller portions have low glycemic loads.
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.
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Source:http://www.dummies.com/how-to/content/how-to-calculate-glycemic-load.html
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