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The glycemic index: Is it the next diet fad?

A food formula originally conceived to help diabetics is poised to become the next diet trend. Phil Lempert has details.

Remember Atkins and South Beach? Of course you do! Those diet regimens, with their emphasis on low carbs and high proteins, have been all the rage with millions of Americans looking to become slimmer and trimmer.

Emphasis on the “have been.”

After two years or so of searching labels for low carbohydrate counts, the growth in sales of low-carb foods has waned. It appears that many followers of the latest food fads found that these “quick-fix” diets weren’t very easy to follow and/or didn’t turn out to be the fix they thought they would be.

While, of course, this probably has as much to do with the dieters as the diet, those eager to fight the flab remain ever-hopeful and are turning to other methods that appear to hold more promise.

And the latest of those, the “glycemic index,” just happens to be one of the foundations of the low-carb diet.

A bit of background: The glycemic index (GI) was originally conceived to aid diabetics. It helps people understand the impact that carbohydrates from individual foods have on blood sugar.

The index is a ranking of carbohydrates (on a scale from 0 to 100) based on their immediate effect on blood-glucose (blood-sugar) levels. The importance of this is that high blood-sugar levels lead to the production of insulin, a hormone that causes the body to store excess carbohydrates as fat.

As most people know, people with diabetes have problems with the amount of insulin in their bodies. The GI was developed for helping people with diabetes choose foods that would not cause big swings in blood-glucose levels.

It did not take long, of course, for dieticians to figure out that the GI could be a useful tool in lowering insulin production in non-diabetics — and thus their levels of body fat.

Eat a carbohydrate that is lower in sugar and contains fiber — blueberries, for example — and the amount of glucose entering your bloodstream comes at a slower and more steady rate. That means fewer blood-sugar spikes, lower insulin levels and, hopefully, less fat.

That’s not the only potential benefit: Not only do people who follow the index tend to lose weight, but researchers have found that it can reduce the amount of LDL (the so-called "bad") cholesterol.

In addition, recent studies from Harvard School of Public Health indicate that the risks of diseases such as type 2 diabetes and coronary heart disease are strongly related to the GI of the overall diet. In 1999, the World Health Organization (WHO) and Food and Agriculture Organization (FAO) recommended that people in industrialized countries base their diets on low-GI foods in order to prevent the most common diseases of affluence, such as coronary heart disease, diabetes and obesity.

That's the good news. The bad is that using the GI is pretty much as complicated as other diets. It is also not a substitute for exercising or eating sensible portions.

Partly, this is because the index alone is not perfect in making day-to-day food choices because it does not take into consideration portion sizes (which, as we all know, are one of the leading causes of American’s obesity problem).

This is why the “glycemic load” (GL) was created. This is a formula that builds on the GI to provide a measure of total glycemic response to a food or meal, taking the quantity of “available carbohydrates” into account. These are carbohydrates that provide an immediate blood-glucose surge — starches and sugar — but little or no fiber.

A typical American diet contains about 100 GL units per day. The formula is based on the Glycemic Load = Glycemic Index (%) x grams of carbohydrate per serving; with one unit of GL having the effect of 1 gram of glucose.

To illustrate the difference, the following grid categorizes some basic foods based on where they fall in a low-medium-high GL to low-medium-high GI ratio based on the data reported in the “Revised International Table of Glycemic Index (GI) and Glycemic Load (GL),” published in the July 2002 issue of The American Journal of Clinical Nutrition.

As always, as with any diet, make sure you consult your physician first and remember that the true keys to effective weight loss are eating smaller portions, eating foods that are lower in fat and sugars and exercising more. There is no miracle diet or quick-fix diet. It is all about understanding what you eat, how much you eat and how you burn off the excess calories.

If you are interested in lowering your daily glycemic load, here are some simple eating tips:

  • Consume breakfast cereals that have a high oat, barley and bran content
  • Consume whole grain breads made with whole seeds
  • Consume all types of fruit and vegetables (except potatoes)
  • Consume plenty of salads and choose those dressings that are low in carbs

Sound familiar? Yes, as noted, keeping to a proper diet is largely a matter of common sense and discipline. The good thing about the glycemic index is that it is a proven formula developed for a medical purpose. In that light, as long as it is seen as a useful tool — rather than a magic bullet — it will no doubt be of great help in America’s battle against obesity.

Phil Lempert is food editor of the “Today” show. He welcomes questions and comments, which can be sent to