The Glycemic Index Diet for Dummies - Meri Raffetto [29]
Looking at portion sizes and carbohydrate grams can give you a better understanding of the glycemic load. Although foods vary, Table 4-1 breaks down the average amount of carbohydrates in each carbohydrate-containing food group based on a particular portion size.
As you can see from Table 4-1, the amount of carbohydrates in a serving of a particular food depends as much on the portion size as it does on the food itself. So consuming 50 grams of carbohydrates (which is definitely more than one serving) will have a dramatic impact on your blood sugar. Take carrots, for example. Carrots have a high glycemic index when cooked (41 to be exact), yet they're considered a nonstarchy vegetable. To consume 50 grams of carbohydrates in carrots, you'd have to eat 5 cups! I don't know about you, but even though I like carrots, 5 cups is a bit much (not to mention it may turn your skin orange). Because the amount of carbohydrates in carrots is so low compared to their average portion size, the glycemic load of carrots is low as well.
On the other hand, a serving of instant white rice, another high-glycemic food with a glycemic index of 72, has around 15 grams of carbohydrates per 1/3-cup serving. To eat 50 grams of carbohydrates in instant white rice, you'd have to eat slightly more than 1 cup of rice — a fairly typical portion size for most people. This portion size means the glycemic load for instant white rice doesn't change much from the food's glycemic index.
The glycemic index compares the potential of foods with equal amounts of carbohydrates to raise blood sugar. The purpose of the glycemic load is to have a usable indicator of the glycemic index that takes portion size into account. Although adding glycemic load to the mix may cause the glycemic index of some foods, such as white rice, to remain the same, it opens up the door for enjoying more foods that may have a high glycemic index but a low glycemic load based on different portion sizes.
Calculating Glycemic Load
Whereas calculating the glycemic index requires human clinical trials (as explained in Chapter 2), the glycemic load is a little simpler to dermine. 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. The next few sections walk you through the basics.
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 × 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: I've rounded the numbers for simplicity's sake. Feel free to do the same in your own calculations.)
45 × 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 × 36 = 2,592 ÷ 100 = 26 glycemic load
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, you can use Table 4-1 as your reference for estimating the amount of available carbohydrates because it gives you the average grams of carbohydrates for the listed portions.
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