The Glycemic Index: Is it a Helpful Weight Loss Tool?

If you stroll through the diet section of your favorite bookstore, you will notice a couple of things.  First, you will see that it takes up a good bit of space!  As you begin to look closer, you will also see that many of the books include “glycemic index” or “blood sugar” in their titles.  What is the glycemic index, and have we finally found the key to easy, permanent weight loss?

The glycemic index is a measure of the blood sugar effect caused by eating a given food relative to eating pure glucose.  Each individual food is given a number from 1 to 100 based on how quickly it converts to glucose in the blood.  Pure glucose has a GI of 100.  The lower an individual food falls on the glycemic index, the slower and less dramatic its blood sugar effect is.  Foods with a high glycemic index include dried fruit, bananas, white bread, ice cream, carrots, and watermelon.  Moderate GI foods include baked beans, green peas, sweet potatoes, blueberries, most pasta, and rice.  Many vegetables, unsweetened yogurt, grapefruit, apples, tomatoes, high-fiber/low sugar cereals, and beans are among the low GI foods.

While the glycemic index can be somewhat useful as a comparative guide to choosing healthier foods, its use as a real life weight loss aid is limited for several reasons.  First of all, the glycemic index rates individual foods, not combinations of foods.  Since we usually eat combinations of foods, like toast with butter and eggs, the actual way that food affects blood sugar is more complex.  Fiber, protein, and fat will slow the passage of glucose into the bloodstream.  Although the overall GI of a high fat diet may be low, it is not likely to be the healthiest way to eat or the best way of losing weight.  A Snickers bar actually rates a lower GI number than a baked potato!  Which do you think is healthier?!

The reliability of the glycemic index is also complicated by the way a food is prepared, the degree to which it is cooked, and the ripeness of produce.  A ripe banana for example, will affect blood sugar more than one that is less ripe.  Even a person’s blood sugar response to the same food can vary from day to day.

The way that the glycemic index is measured can also contradict a common-sense approach to healthy eating.  Since the rating is determined using the amount of a given food containing 50 grams of carbohydrate, some of the quantities containing that amount can be unrealistically large.  In the case of carrots, most of us would be sick before we could eat enough of them to get 50 grams of carbohydrate.  Carrots are a very healthy food, yet many people wonder if they should be eating them because they have a high glycemic index.  Please do not stop eating carrots!

Losing weight still depends on a negative energy balance.  In other words, you have to burn more calories than you eat in order to lose weight.  Taking a broad look at the glycemic index, some generalizations can be helpful.  It is true that choosing plenty of high fiber low calorie foods, like fruits and vegetables, is a good weight loss strategy.  These foods also tend to be low on the glycemic index.  A moderate amount of high protein foods, which also tend to be low GI foods, can be helpful because protein seems to help satisfy hunger.  The actual GI numbers are less important than these more general guidelines for healthy weight control.  Just beware of the low GI high fat foods!  They are still concentrated sources of calories, despite their low GI rankings.  While the glycemic index is not the “magic bullet” for weight loss, the good news is that there is nothing wrong with carrots or bananas.


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