The idea that all carbohydrates are not created equal has become the foundation of many popular diets. Some argue that foods like white bread and potatoes, which have a high so-called glycemic index because they spike blood sugar and insulin, should be avoided in favor of more healthful carbs like whole grains and non-starchy vegetables. But rigorous new research from the National Institutes of Health suggests that for people who already follow a healthful diet, the glycemic index may not be very important. Frank Sacks, professor of medicine at Brigham and Women’s Hospital, led the research. David Ludwig, professor of pediatrics at Boston’s Children’s Hospital, is quoted.