One of the most misunderstood and confusing parts of a low-glycemic diet is the difference between the “glycemic index” and the “glycemic load” of a food. Most glycemic food charts list both the “GI” and the “GL” of each food. Understanding the difference between the glycemic index and glycemic load can broaden the different kinds of foods you can eat.
The GI is a system of measuring the body’s blood sugar response to equal amounts of carbohydrate in foods such as bread, pasta, rice, fruits, peas, beans, yogurt, milk, and vegetables. Note the GI is calculated for a food portion containing 50 grams of carbohydrate in each food. That isn’t a serving size of 50 grams of food (about 2 ounces). It’s a serving size of however much food it would take to contain 50 grams of carbohydrate in that particular food. Foods vary widely in how much carbohydrate they contain, and sometimes the resulting glycemic index number can be a little deceptive.
Take watermelon for example. Watermelon has a GI of 75, a very high glycemic index. Based on that GI alone, you might never eat watermelon. But the GI is based on eating 50 grams of carbohydrates in watermelon. How much watermelon is that? It turns out to be a lot of watermelon.
A normal slice of watermelon only has about 6 grams of carbohydrate. Most of watermelon is water. So while eating 50 grams of watermelon carbs would quickly spike your blood sugar, you would have to consume 8-9 good size slices of watermelon…more than a pound of watermelon and more than the average person eats.
So the glycemic load was developed to predict blood sugar spikes based on normal serving sizes. In the case of watermelon, that serving size is calculated to be 120 grams of watermelon…about 4 ounces, or one slice. When watermelon is viewed from the point of view of eating a single slice, the effect on blood sugar is low. Thus, the glycemic load of watermelon is 4…a very low GL and a food that is OK to eat.
Another example is carrots.
Cooked carrots have a GI of 92…about as much as raw sugar. Again, based on the GI alone, carrots would be a food most people would avoid. But the GI is based on eating enough carrots to consume 50 grams of carbohydrates. Thus the question is, how many carrots would that be?
In order to eat 50 grams of carbohydrate in carrots, you would have to eat over a pound and a half of carrots, because each carrot is very low in carbohydrates. Very few people would eat that many carrots. Therefore, the normal serving size of carrots was estimated to be 80 grams, or about 3 ounces…the weight of 1-2 carrots. If you eat one carrot, the glycemic load (the actual effect on blood sugar) is very low, because individual carrots are low in carbohydrates. It takes a lot of carrots to get 50 grams of carbohydrates to spike your blood sugar.
Now lets compare those numbers to a bagel. A bagel has a GI of 72, just a few points below watermelon. But you’ll get 50 grams of carbohydrate eating just one bagel, so eating a “normal” serving of bagel will give you the full blood sugar spike that a GI of 72 predicts. That’s why a bagel has a glycemic load of 25, which is high.
A GL greater than 20 is considered high, a GL of 11-19 is considered medium, and a GL of 10 or less is considered low.
So here’s what you need to remember. Foods that have a low GI almost always have a low GL. But foods with an intermediate or high GI may range from low to high GL—it all depends on the suggested serving size. So peas have a glycemic index of 54. Left with only that GI number, you would avoid peas. But peas are low in carbohydrates, so you’d have to eat a ton of peas to spike your blood sugar. That’s why the GL, the glycemic load, is so important. For peas, the GL is listed as “4” for a 3-ounce serving. You can have peas. You can even eat 6-ounces of peas and have a GL of 8…still well below the low rating of 10 or below.
Again, low GI foods almost always have a low GL. But learning to check the GL of intermediate to high GI foods will only expand the types of foods you can eat. That’s why ice cream, which has a GI of 80, is OK to eat on a low-glycemic diet. Ice cream is high in fat and stocked full of a lot of good milk proteins. It does have sugar, but a relatively small amount in relation to its other ingredients. So if you look at the serving size on a glycemic load chart, ice cream is listed as an 80 gram serving…about 4 ounces. If you keep to this serving size, the glycemic load is only 10. You can enjoy ice cream as a healthy, low-glycemic treat in satisfying, manageable quantities.
I hope this makes sense. Here is a list of some other intermediate and high GI foods that have few carbohydrates in a normal serving, and therefore have a low glycemic load and are OK to eat on a low-glycemic diet:
Pumpernickel bread, glycemic index 50, glycemic load 6
Whole wheat bread, glycemic index 71, glycemic load 9
Apple, glycemic index 38, glycemic load 6
Peach, glycemic index 42, glycemic load 5
Microwave popcorn, glycemic index 55, glycemic load 6 (serving size about 1 ounce popped corn)
Honey, glycemic index 60, glycemic load 10 (serving size about 1 ounce honey)
Whole grain baguette (like Semifreddi’s), glycemic index 73, glycemic load 9
Cherries, glycemic index 63, glycemic load 9
You get the point. Low GI foods are a no-brainer. Intermediate and high-GI foods can be added to a low-glycemic diet if they are naturally low in carbohydrates and have a low GL number for a specific portion size.