The glycemic index has been a popular tool for years. Yet a fair amount of research has revealed significant holes in it’s utility. Can the GI be trusted to aid in actually controlling your blood sugar? I won’t cover how this effects body composition because you know my stance on this subject. (TL;DR carbs are no more fattening than fats or protein)
I shall cover 2 main issues with the GI.
- How do foods with varying GI’s affect the glycemic response?
- How accurate is the GI?
GI and Glucose Stuff
I came over a new study that examined the glycemic response to fast and slow digesting carbohydrates. A fast digesting carbohydrate, according to the GI will result in a large glycemic response. A slow digesting carbohydrate, according to the GI, results in a slower glycemic response. This is what the GI says. What does good ole science say?
The researchers sought out to find out if fast and slow digesting carbohydrates actually resulted in a different glycemic response. They tested 10 healthy dudes. So one could bitch incessantly how this doesn’t apply to:
- The list goes on and on.
The study used enriched wheat bread or pasta. The researchers looked how these foods affected ‘rate of appearance of exogenous glucose (RaE), endogenous glucose production, and glucose clearance rate (GCR). In addition, postprandial plasma concentrations of glucose, insulin, glucagon, and glucose-dependent insulinotropic polypeptide (GIP) were analyzed.’
According to the GI the results would be probably be something like this: Pasta has a higher GI than Wheat bread according to the study, as the rate in which glucose was present in the blood was faster in bread. Since the pasta has a higher GI, you would expect a larger spike in glucose as it enters the bloodstream.
There were obviously other factors at work though, as this isn’t what happened. The two foods actually had similar glycemic responses. How can this be?
Since the low glycemic foods elicited a lower insulin response the GCR glucose clearing rate (from the blood stream) was slower than the rapid digesting carbohydrate. The fast digesting carbohydrate had a faster GCR because it had a higher insulin response.
Even though a given carbohydrate can cause varying GIP and insulin secretions a similar glycemic response can occur.
The second part of this will be shorter. In my first blog entry I wrote about how different GI’s will have different values on different indices. I mentioned that I found the GI of carrots on two different indices. One had them valued at 47 and the other at 90. That’s a very large difference.
Another study looked at this very subject. They found that whole meal GI values were 22-50% overestimated over the actual value. GI for individual foods were also overestimated. So take that for what it’s worth… Which is a lot by the way.
The lack of accuracy in the GI has implications on the GL as well. GL is sometimes looked as a more “polished” version of the GI, as it takes into account the volume of food needed to illicit a blood glucose spike. For instance, watermelon has a reasonably large GI score of ~70 (give or take 35, heheh) but the GL is only 4(this number would also be skewed). So watermelon isn’t all that bad, because you’d have eat a disgusting amount of it in order to actually raise your blood glucose.
Yet, if the GI is not accurate then GL will not be accurate as well. So using these charts is really quite fruitless.
Oh and by the way, GI will be different for people with differing insulin responses. So peoples’ glucose will be transported out of the blood stream faster than others, even with the same food. So all in all, the GI is pretty much.. Meh.
What To Do With This
There are two major knocks against the GI. Does this make the GI useless? I personally don’t use the GI, glycemic load (GL), or insulin index (II). If you just focus on eating whole foods rather than the usual crap that comes in a box, you will probably have the same results as following a damn index.
The researchers in the first study cited concluded “These types of starchy products cannot be identified by using the glycemic index and therefore another classification system may be necessary.” Another useless classification system is not needed because it will be another set of particulars that nobody will follow.
I’m not an RD, so I can’t dispense information about helping people control their diabetes. I can however give my opinion based on what I’ve seen from research. I have yet to see a low carbohydrate diet that didn’t drastically reduce fasted blood glucose levels. Yet for some reason, RD’s never suggest these kinds of diets to their clients. I have no idea why that is.
In terms of fat loss, I’d guide you to this. You can eat carbohydrates and lose weight. No question about that.
If you’re trying to gain muscle mass… You know what to do… Consume carbohydrates, all of them, in the entire world.