Popular diets such as Atkins and South Beach recommend eating low or no carbohydrates to lose weight. But not all carbs are created equal, and now evidence suggests that using the "glycemic index" may be the way to shed pounds and boost health.

Results of a new animal study found that a low-glycemic-index diet can lead to weight loss, reduce body fat, and trim risk factors for diabetes and heart disease.

The glycemic index ranks carbohydrates based on their immediate effect on blood sugar levels. Carbohydrates that break down quickly during digestion have the highest glycemic index. Carbohydrates that break down slowly, releasing sugar gradually into the blood stream, have a low glycemic index.

The theory is that the rapid increase in blood sugar makes you hungry and causes you to eat more and gain weight. Meanwhile, carbs that release their sugar more slowly keep your hunger in check.

"Contrary to popular belief, starchy foods can be broken down to sugar very quickly," said lead researcher Dr. David Ludwig, director of the Optimal Weight for Life Program at Children's Hospital Boston. "White bread, breakfast cereals, potatoes, have a very high glycemic index, whereas fruits, vegetables, nuts and legumes have a low glycemic index," he added.

According to Ludwig, previous studies in humans have suggested that low-glycemic-index diets can have important health benefits. "But these studies have had difficulty in distinguishing the effects of glycemic index from those of other dietary factors like protein and fiber," he said.

Partly for this reason, no agency in the United States recognizes the glycemic index in human nutrition, Ludwig said. The glycemic index is recognized by many other countries and by the World Health Organization, he said.

To determine the effect of a low-glycemic-index diet in a controlled setting where the diet could be tested without interference from other factors, Ludwig's team experimented with rats.

In the experiment, rats were fed a diet of 69 percent carbohydrates. Eleven rats were randomly assigned to a high-glycemic-index diet and 10 to a low-glycemic-index diet, according to the report in the Aug. 28 issue of The Lancet.

After two to four months, the researchers found that the rats given the high-glycemic-index diet had 71 percent more body fat and 8 percent less lean muscle mass, compared with rats on the low-glycemic-index diet.

In addition, the high-glycemic-index group had significantly higher blood sugar and insulin levels and higher triglyceride levels, compared with the low-glycemic-index group.

In further experiments, rats were switched from a low- to a high-glycemic-index diet. These rats had greater increases in blood sugar and insulin, compared with animals switched from a high- to low-glycemic-index diet.

"These findings suggest that low-glycemic-index diets might help prevent and treat obesity, diabetes and heart disease," Ludwig said.

A healthful diet, according to Ludwig, includes adequate protein, healthy fats and carbohydrates that have a low-glycemic-index -- such as fruits, vegetables, nuts, whole grains and legumes.

There have never been any adverse effects from a low-glycemic-index diet, Ludwig added.

"In contrast, low-fat diets can raise bad cholesterol and lower good cholesterol," he said.

"A low-glycemic-index diet is the perfect compromise between a low-fat diet and an Atkins-type, very low carbohydrate diet," Ludwig said.

Dr. Mary Vernon, a spokeswoman for Atkins Nutritionals Inc., and co-author of the Atkins Diabetes Revolution, said, "The Atkins diet doesn't say eat meat and eat a candy bar to get your carbohydrates."

Vernon said the diet recommends limiting carbohydrates to 20 grams per day until you lose the weight you want, and then increasing your intake of carbohydrates until you see that you are starting to gain weight.

"The Atkins diet recommends certain carbohydrate sources, which are all low-glycemic-index sources," Vernon said. "Carbohydrates with a low glycemic index are healthy carbs with nutritional value, not just energy value," she added.

More information

To learn more about the glycemic index, visit the Joslin Diabetes Center.

Reference Source 101
August 27, 2004

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