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3 Things the Glycemic Index Doesn't Tell You

Posted by Greg Kester on

The popularity of low glycemic foods and dieting has put the glycemic index into the spotlight. The glycemic index is a measure of how an individual food item affects blood sugar—the higher the number, the greater the effect—and many people have come to use it as their nutritional “measuring stick.” However, by itself, the glycemic index is actually a very poor marker of a food’s nutritional quality. Let's take a look at:

3 Things the Glycemic Index Doesn't Tell You

1. How healthy a food is

Peanut M&M’s have a glycemic index of 33. Oranges have a glycemic index of 40. We trust you know which is a healthier option. Just because one food’s glycemic index is lower than another’s doesn’t tell you anything about their nutritional quality or effects on health. It’s important to look at a food’s nutrient density (vitamin and mineral content), and whether it contains harmful additives or trans-fat.

2. How a realistic serving size of a food affects blood sugar

Low Glycemic Salmon Salad
The glycemic index tells you how much a certain amount of a food item, eaten by itself, affects blood sugar, but that “certain amount” isn’t always a realistic serving size. Keep in mind that to determine a food’s glycemic index, it must be fed to a test subject in an amount that provides 50 grams of digestible carbs. Snickers bars and parsnips have similar glycemic index values (51, and 52, respectively). However, to obtain these values, test subjects were required to eat only one and half Snickers bars but almost three cups of sliced parsnips (mmmm...parsnippy). This is because one standard-sized Snickers bar contains 32 grams of digestible carbs, whereas a cup of sliced parsnips contains only 17 grams. In other words, the carbohydrate density of parsnips is much lower than that of Snickers.

​This is where the concept of glycemic load comes in. Glycemic load accounts for a food’s carbohydrate density to better represent how a realistic serving size will affect blood sugar. The glycemic load for Snickers is 18, compared to only 4 for parsnips.Bottom line: the glycemic load is a better measure of how a food item (at a realistic serving size) will affect your blood sugar.

3. How much a food affects insulin levels

You might think that the effect of a food on insulin levels is directly proportional to its effect on blood sugar, but this isn’t necessarily the case. Certain high protein foods, including meat, actually cause a significant rise in insulin, despite having only a very small amount of carbs and a negligible effect on blood sugar. Why does this matter? Insulin plays a huge role in determining how your body deals with the energy derived from the food you eat.

​Too much or too little insulin can be a bad thing. Too much insulin will lead to excess fat accumulation. Too little insulin and your blood sugar will become dangerously high. Some evidence suggests that in the long-term, very high protein diets may actually contribute to insulin resistance, despite the fact that they don’t “spike” blood sugar.Bottom line, even if a food has a low glycemic index, it can still increase your insulin levels.

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