With the talk about this going on in the
Watermelon thread, I thought I'd post some info I found about Glycemic Load (GL) to help de-mystify it a bit for all of us.
This is from
Diabetes Self-Management
Quote:
One other “downside” of the GI [Glycemic Index] is that fact that the ranking system doesn’t take into account the amount of food one eats. Here’s an example. People are often surprised to see that carrots, much like watermelon, have a high GI. The inclination is to stop eating carrots. But think back to your nutrition class in school—carrots are good for you! Besides being low in calories, high in fiber, and rich in beta-carotene, a half-cup of carrots has just 8 grams of carbohydrate. So why does it have a high GI?
The GI was originally developed by researchers for research purposes, and it was calculated from servings of food that contained 50 grams of carbohydrate. [bolding mine] In the case of carrots, you’d have to eat about 1 1/2 pounds to get that much carbohydrate! Would you eat that many carrots at one time? Probably not. The GI doesn’t take into account realistic serving sizes. However, the glycemic load does.
Glycemic load (GL) is the amount of carbohydrate in a food multiplied by that food’s GI. The GL is also a ranking of how foods affect blood glucose levels, but unlike GI, the GL takes serving size into account. Like GI, the lower the GL, the lower the spike in blood glucose levels. Low-GL foods have a value of 10 or less; moderate-GL foods have a value of 11-19; and high-GL foods have a value of 20 or more.
Back to the carrots, then. Carrots have a GI of 71. If we multiply the 8 grams of carb in a half cup by .71, we get a GL value of roughly 6. Therefore, carrots are a low-GL food. This means that, unless you truly are going to eat a pound and a half at a time, carrots don’t have a big impact on blood glucose levels.
I believe Dr. A does take Glycemic Load (GL) into account--that's why we're allowed to have medium-sized bananas, but not large ones. In fact, it's why he changed the list to allow for bananas in the first place. Their GI is high, but the GL of a medium one is okay. However, I'm not sure what the thought is about corn. I agree with Cyndi, that it might be because corn is in so many things. We are allowed air-popped popcorn in P2, though, so he obviously thought about it at some point. Is anyone on a site where they can submit a question to Dr. A about it?
Although GL is highly recommended as a way to manage blood sugar for diabetics, there are some concerns about whether using low GL foods can help with weight loss:
Quote:
Das et al. conducted a study on 36 healthy, overweight adults, using a randomised test to measure the efficacy of two diets, one with a high glycemic load and one with a low GL. The study concluded that there is no statistically significant difference between the outcome of the two diets. However, this might simply be due to the small sample size (n=36). In the study, the low GL diet did provide the most weight loss on average, but not enough to clear the bar of "statistical significance". See Das et al. (2007). "Long-term effects of 2 energy-restricted diets differing in glycemic load on dietary adherence, body composition, and metabolism in CALERIE: a 1-y randomized controlled trial" American Journal of Clinical Nutrition, Vol. 85, No. 4, 1023-1030
This chart gives you some really good information in comparing GI and GL. The first number in the parentheses is the G
L and the second is the G
I. The article that accompanies the chart can be found
here.
There's a lot to think about with all this...I think sticking to the SBD guidelines, overall, is the best way to start. Then, if you want to try other things to see how your body reacts, using the GL lists can really help you pick ones that are less likely to affect you.
The one thing to remember is that, unlike the GI, the GL is based on portion/serving size. So if you eat more than the serving size, you can assume that the GL of what you've eaten will be different. Therefore, when trying these things, you need to stick to serving size.