April 6, 2007

The Glycemic Index: Good Carb, Bad Carb

Written by Caroline Cederquist, M.D.

If you're one of those people who can't stand all the counting and tracking and adding and charting that some diets require, you could find a refuge in one simple numerical scale: the glycemic index. On the other hand, you might find it another maddening way to complicate the simple act of eating.

The glycemic index is a measure of the quality of carbohydrate foods. It's kind of a good carbs/bad carbs thing, based on how they affect your blood sugar. Though it's not new, it did start getting a lot of press when the anti-carb movement took hold.

It works like this: in the glycemic index, pure glucose is arbitrarily assigned the score of 100; it doesn't mean anything in particular; it's just a set reference point for how it has affected the blood sugar by about two hours after eating. Then all other foods in the index are given a number relative to glucose and its affect on the blood sugar.

Foods with a low index typically break down slowly and don't cause drastic fluctuations in blood sugar. Foods with a high index typically do. For instance, green peas have an index of 39, while corn flakes have an index of 92.

Originally developed to help folks—particularly diabetics—control their blood sugar, the index includes mainly carbohydrate foods, because protein and fat don't have much immediate effect on blood sugar.

But assigning numbers to different foods based on their glycemic effect just happens to create a scaled list of foods that ends up being a very useful tool for people dealing with obesity and other health issues, as well. That's because simply maintaining a low-glycemic index diet tends to guide people toward healthier eating and weight loss, even when that is not their specific goal.

Consider: Type II diabetes, as well as various cancers and cardiovascular disease, are all highly correlated with high index diets. There's abundant research that shows that reducing the overall glycemic index also reduces the risks of those problems.

That's because almost by default, a low-index diet will include more fresh fruits and vegetables, more fiber, more dairy, all foods that offer essential nutrients, that are more likely to be lower in calories and which tend to keep the body sated longer, holding off the next hunger spell. All that usually adds up to weight loss, no matter what the program.

Proponents of the index say it's more helpful than counting calories or grams of fats or carbs, and actually offers a simplified approach to learning to eat better, but some experts caution that people shouldn't get too wrapped up in worrying about the precise numbers. Instead, they urge that people pay attention to whether the foods they're eating have a low, medium or high index.

That's because, as with any rule, there are exceptions to the fairly consistent physiological rules that underlie the index. For instance, watermelon has a pretty high glycemic index, about 75, which is even higher than table sugar. Does that make it bad for you? No. Because in spite of its high index, watermelon actually has a pretty low glycemic load. That's a measure based on the amount of food you'd actually consume, not just an arbitrary quantity used in testing, as with the index.

The glycemic load of a food can be determined using the glycemic index number for a food, divided by 100 and multiplied times the available carbohydrate you'd eat. With most foods, low index is consistent with low load, but there are the quirky exceptions. Of course, to find them, you'd be back to doing a bunch of math again, and that's just not the way people normally eat.

That's why doctors and nutritional experts encourage people who are trying to develop a healthy diet to avoid getting caught up in the numbers game and look more generally at the foods in the index, leaning toward those at the low end. Anything over 70 is considered high index, 55 through 69 is medium and below 55 are foods with a low glycemic index.

And look what's in those groups: high index foods include most breakfast cereals, white breads and other processed baked goods, most potatoes, ice cream, candies and table sugar, your veritable Atkins nightmare.

Lower index foods include cherries, grapefruit, broccoli, legumes like lentils and beans, most whole grain baked goods and most dairy foods. So even without counting calories or keeping track of specific index numbers, you can see that steering your diet toward the low end of the index is bound to do you good.

We like to encourage patients to think of glycemic index and glycemic load as just two more tools that can be helpful in developing healthier thinking and planning about dietary habits.

A final thing to remember: there's not one standardizedglycemic index list and most indexes include brand-name items that people buy on a typical shopping trip, as well as the more generic items like vegetables and fruits. This is one of the more helpful aspects of the lists, but only if you get one that relates to where you live.

If your average Southwest Florida resident looked at an index created in Australia, it wouldn't be much help, because really, when's the last time you had a couple Golden Pikelets with a nice glass of Milo?


Fruits tend to have a high glycemic index, so I recommend that people take their fruits with a meal, or with some protein like cottage cheese or regular cheese. These protein sources help mitigate the fruits glycemic effect. Don't let a high index number keep you away from your apple a day.

About The Author:

Caroline J. Cederquist, M.D. is a board certified Family Physician and a board certified Bariatric Physicians (the medical specialty of weight management). Dr. Cederquist is the founder of Bistro MD formerly Diet To Your Door, a home diet delivery program that specializes in low calorie gourmet food that is delivered to your home or office. Bistro MD serves as culmination of Dr. Cederquist's expertise and experience in the world of medical weight loss.

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