Lyle McDonald

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October 21, 2016

Carbohydrates Part 3: Problems with the GI

So after a couple of weeks of nothing, it’s time to continue this series, which will invariably run to 4 parts because that’s just how I do things (tediously and in an overwritten fashion).

As an overview of last time, I described how the Glycemic Index (GI) is measured along with the implications that it had for diabetes treatment, potentially weight loss and for athletes.  The main take home is that, the development of the GI had an impact on diabetes treatment but was a huge hassle to use.

For weight loss, studies were about half and half on whether or not low GI foods (typically higher in protein and fiber) were more filling or not.  So far as athletes, the benefit of high and low GI are context specific while the physique athletes were the ones who really got hung up on the GI based on what would turn out to be an incorrect assumption about insulin dynamics (discussed today).

Problems with the GI

While the GI concept made a lot of sense in that carbohydrates would digest and impact on blood glucose differently, there were a lot of problems with the method.  Perhaps the largest was the most obvious: feeding someone 50 grams of digestible carbohydrate after an overnight fast isn’t really that relevant to how people eat in the real world in a number of ways.

Problem 1: Only One Meal is Eaten After Fasting

Yes, fine, breakfast by definition occurs after an overnight fast but are measurements made at that single time point indicative of the rest of the day?  It turns out that the answer is no.And it was found early on that there was a second meal effect, that how the body responded to the next meal of the day could be profoundly different.  In one study, a low glycemic dinner changed the glycemic response to breakfast on the next day.

Read the rest of Carbohydrates Part 3: Problems with the GI

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