Is the Glycemic Index Overrated?

July 19, 2006 08:38 AM

By Jim Brown, Ph.D., Author, Tennis: Steps to Success, and Amanda Carlson, M.S., R.D., Nutrition Manager & Research Coordinator, Athletes’ Performance

No wonder everyone is so confused about nutrition, weight control, and health. Another media blow up has occurred involving the Glycemic Index. Could it be true? Could the index that has been adopted by many as the “golden ticket” to weight loss be skewed?

The Glycemic Index has been a trendy topic, and the term has even worked its way into many of our water cooler conversations. Two years ago hardly anyone had heard of the GI, which ranks carbs according to their ability to affect blood glucose. However, these days most people have heard of this index and have some idea of what it means.

The Premise

The premise of using the GI in weight control is that diets that are low in the index will help people lose weight and reduce their risks for both heart disease and diabetes. The original studies evaluating the GI of different foods were conducted in a controlled environment on subjects who had fasted overnight. They ate a single specific carbohydrate in a prescribed amount and had their blood glucose measured two hours later. In a controlled environment, when a low GI carb is eaten, it is broken down more slowly, which produces a more consistent glucose level. A high GI carb is just the opposite. It is broken down quickly and causes a large spike in blood glucose, followed by a subsequent blood glucose crash. A moderate GI falls somewhere in the middle. The problem is that the science doesn’t really apply to real life because breakfast is the only time we truly eat after a fast, and additional factors such as the length of time the food is cooked, your own body’s hormones, and any other food (protein or fat) that is eaten in combination with that carbohydrate can alter how the body uses glucose.

Mixed Signals

The real picture of the research is that it is mixed. Some studies show beneficial effects of low GI diets on diabetes and other conditions, and some don’t. A recent study conducted at the University of Southern California found that those who followed a diet of lower GI carbohydrates did not have significantly lower blood glucose levels than those who followed a diet of relatively high GI carbs. Does this mean to run out and get that Wonder Bread that you have been dreaming about since starting to eat healthier carbs? No! Lots of studies link dietary fiber to a decreased risk of heart disease, diabetes, and obesity. This questions whether it is really the GI of the food that makes a food healthy or the components of the food that make it fall low on the Glycemic Index. Foods that are low on the GI are typically higher in fiber. Therefore, many of the studies linking GI to good health may have, in fact, reflected the dietary fiber found in those foods.

The Big Picture

For all of you who jumped on the Glycemic Index bandwagon, don’t get off just yet. The Glycemic Index has taught us a lot about carbohydrates by helping us realize that all carbs are not created equal. However, the Glycemic Index is not the complete answer to controlling weight, preventing heart disease, or managing diabetes. It is simply one piece of the puzzle.

The bottom line is that foods that are found lower on the GI tend to be more whole foods, with more nutrients, and more fiber. People should know about the Glycemic Index, but at the end of the day they should “come back to earth” and choose the least processed form of food possible. Don't make it complicated. When choosing carbs, reach for fruits, veggies, beans, and whole grains. When you are shopping for breads and cereals, look for fiber. If the cereal or bread has three or more grams per serving, go for it. If it doesn't, look for something else.

Look at the big picture in your quest to achieve a healthier lifestyle by including whole grains, fiber, fruits, vegetables, lean proteins, and healthy fats, rather than looking at one tool to choose foods.