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Is glycemic index irrelevant?

Posted Feb 14 2010 9:05am


University of Toronto nutrition scientistDr. David Jenkinswas the first to quantify the phenomenon of "glycemic index," describing how much blood sugar increased over 90 minutes compared to glucose. The graph is from their 1981 studyThe glycemic index of foods: a physiologic basis for carbohydrate exchange. The research originated with an effort to characterize carbohydrates for diabetics to gain better control over blood sugar.

Since Dr. Jenkins’ original workthousands of clinical studies have been performed by others exploring this concept. The food industry has also devoted plenty of effort exploiting it (e.g.low-glycemic index noodleslow-glycemic index cerealsetc.).

Most Americans are now familiar with the concept of glycemic index. You likely know that table sugar has a high glycemic index (60)increasing blood sugar to a similar degree as white bread (glycemic index 71). Oatmeal (slow-cooked) has a lower glycemic index (48)since it increases blood sugar less than white bread.

A number of studies have shown that when low glycemic index foods replace high glycemic index foods (e.g.whole wheat bread in place of cupcakes)people are healthier: less diabetesless heart attackless high blood pressure. Books have been written about glycemic indextouting its benefits for health and weight control. Health-conscious people will try to substitute low-glycemic index foods for high-glycemic index foods.

So what’s not to like here?

There are several fundamental flaws with the notion that low-glycemic index foods are good for you
1) Check your blood sugar after a low-glycemic index food like oatmeal. Most non-diabetic adults will show blood sugars in the 140 to 200 mg/dl range. The more central (visceral) fat you havethe higher the value will be. In other wordsan apparently “healthy” whole grain food like oatmeal can generate extravagantly high blood sugars. Repeated high blood sugars of 125 mg/dl or greater after eating increase heart disease risk by 50%.

2) Foods like whole wheat pasta have a low glycemic index because the blood sugar effect over the usual 90 minutes is increased to a lesser degree. The problem is that it remains increased for an extended period of up to several hours. In other wordsthe blood sugar-increasing effect of pastaeven whole grainis long and sustained.

3) Low-glycemic index foods trigger other abnormalitiessuch as small LDL particlestriglyceridesand c-reactive protein (a measure of inflammation). While they are not as bad as high-glycemic index foodsthey are still quite potent triggers.

Low-glycemic index foods trigger the very same responses as high-glycemic index foods—they’re just less bad. But less bad does not equate to good. Low-glycemic index foods cause weight gaintrigger appetiteincrease blood pressureand lead to the patterns that cause heart disease.

High-glycemic index foods are bad for you. This includes foods made with white flour (bagelswhite breadpretzels). Low-glycemic foods (whole grain breadwhole wheat crackerswhole wheat pasta) are less bad for you—but they are not necessarily good.

Don’t be falsely reassured by foods because they are billed as “low-glycemic index.” View low-glycemic index foods as indulgencessomething you might have once in a whilesince a slice of whole grain bread is really not that different from a icing-covered cupcake.
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