A new animal study has found that a diet in which carbohydrates are low in sugar or at least slow to release sugar can lead to weight loss, reduced body fat and reduced risk of diabetes and cardiovascular disease risk.

Such diets have a low glycemic index. Many studies have suggested that a diet with a low-glycemic index is beneficial. However, due to the design of these studies, the benefits could have come from other aspects of the subjects' diets. As a result, no major health agency or professional association refers to glycemic index in their dietary guidelines.

As reported in the August 28th issue of the Lancet, study author David Ludwig, MD, director of the Optimal Weight for Life program at Children's Hospital Boston, and his colleagues fed rats tightly controlled diets with identical nutrients, except for the type of starch.

Both diets were 69 percent carbohydrates, but 11 rats were randomly assigned to a starch high on the glycemic index and 10 to a starch low on the glycemic index. Food portions were controlled to maintain the same average body weight in the two groups.

At follow-up, the group on the high glycemic index diet had 71 percent more body fat and 8 percent less lean body mass than group on the low glycemic index diet, despite very similar body weights.

The fat in the high glycemic index group was concentrated in the trunk area, conferring "the apple shape as opposed to the pear shape," Ludwig said, noting that having an apple shape is a known risk factor for cardiovascular disease in humans.

The high glycemic index group also had much greater increases in blood glucose and insulin levels and far more abnormalities in the pancreatic islet cells that make insulin, all changes that occur in diabetes. Finally, the high glycemic index group had blood triglyceride levels nearly three times that of the low glycemic index group, a risk factor for cardiovascular disease.

"What the study shows is that glycemic index is an independent factor that can have dramatic effects on the major chronic diseases plaguing developed nations – obesity, diabetes and heart disease," said Ludwig. "This is the first study with hard endpoints that can definitively identify glycemic index as the active dietary factor."

Unlike the popular Atkins diet, which seeks to minimize carbohydrate intake, the low glycemic index diet makes distinctions among carbs. It avoids high glycemic-index foods, such as white bread, refined breakfast cereals and concentrated sugars, which are rapidly digested and raise blood glucose and insulin to high levels. Instead, it emphasizes carbohydrates that release sugar more slowly, including whole grains, most fruits, vegetables, nuts and legumes.

"The Atkins diet tries to get rid of all carbohydrates, which we think is excessively restrictive," said Ludwig. "You don't have to go to this extreme if you pay attention to the glycemic index and choose low glycemic index carbs."

Researches are now seeking recruits for a large human study on low glycemic index diets.

Other sources:Children’s Hospital Boston