The Atkins alternative
First came low-fat diets, then came low-carb diets. Now David Ludwig, MD, PhD, director of Children's Hospital Boston's Optimal Weight for Life (OWL) obesity program, is weighing in on the low-glycemic-index (low-GI) diet, which focuses on carbohydrates that are low in sugar or release sugar slowly.
Ludwig's team conducted a tightly controlled animal study in which rats were fed diets with identical nutrients, except for the type of starch. Eleven rats were randomly assigned to a high-GI starch and 10 to a low-GI starch. At follow-up, the high-GI group had 71 percent more body fat and 8 percent less lean body mass than the low-GI group, despite very similar body weights. The high-GI group also had significantly greater increases in blood glucose and insulin levels on an oral glucose tolerance test, and far more abnormalities in pancreatic islet cells. Finally, their blood triglyceride levels were nearly three times higher than those of the low-GI group.
Results were similar when the experiment was repeated using a crossover design, with rats switching from one diet to the other, and the findings were further validated in mice. The study was published in The Lancet on August 28.
Many previous studies, including small-scale human studies, have suggested that low-GI diets are beneficial, but they didn't control for other aspects of subjects' diets, such as fiber or overall caloric intake. For this reason, Dr. Ludwig says, no major health agency or professional group references glycemic index in its dietary guidelines. He hopes his new findings will help change that.