The low-glycemic-load (low-GL) diet reduces carbohydrates that are rapidly digested and that raise blood sugar and insulin to high levels -- such as white bread, refined breakfast cereals, and concentrated sugars. Instead, it emphasizes carbohydrates that release sugar more slowly, including whole grains, most fruits, vegetables, nuts, and legumes. "Our data suggest that the type of calories consumed - independent of the amount - can alter metabolic rate," says Dr. David Ludwig, director of the Optimal Weight for Life (OWL) obesity program at Children's Hospital Boston and the study's senior investigator. "That hasn't been shown before. The idea that 'a calorie is a calorie is a calorie' doesn't really explain why conventional weight-loss diets usually don't work for more than a few months."
Ludwig and colleagues randomized 46 overweight or obese adults aged 18 to 40 to consume one of two diets: a standard low-fat diet or a low-GL diet. Both diets provided approximately 1500 calories/day and were designed to produce a 10% weight loss in 6 to 10 weeks. However, the low-GL diet was higher in fat and made various carbohydrate substitutions, such as steel-cut oats instead of instant oatmeal, blueberries instead of raisins, and cracked-wheat bread instead of tortilla chips.
The 39 subjects who remained in the study succeeded in losing about 10% of their initial body weight. The low-GL dieters had smaller decreases in resting energy expenditure (averaging 96 kcal/day, or 5.9%) than the low-fat dieters (averaging 176 kcal/day, or 10.6%), meaning their metabolism did not slow as much. They also reported less hunger each day while on their diets.
"Almost anyone can lose weight in the short term - very few keep it off in the long term," says Ludwig. "That's given rise to the notion that the body has a 'setpoint' - and that when you diet, internal mechanisms work to restore your weight to that setpoint. A low-GL diet may work better with these internal biological responses to create the greatest likelihood of long-term weight loss."
Confirming other research, Ludwig's team also found that the low-GL group had significantly greater improvements in insulin resistance (a risk factor for diabetes) and serum triglyceride and C-reactive protein levels (risk factors for cardiovascular disease). They now have a long-term study, in a larger group of subjects, to see if people on the low-GL diet can indeed keep off the lost pounds.
Dr. Mark Pereira of the Children's Hospital Boston Department of Medicine (now at the University of Minnesota) was first author on the study.
Children's Hospital Boston is recruiting adults for a large-scale, 18-month study of the low-GL diet. Subjects will receive comprehensive dietary and behavioral counseling in individual and group sessions that will enable them to put low-GL diets into effect. Subjects must be overweight, 18 to 35 years old, and motivated to attend weekly sessions for four months. People interested in enrolling should contact Erica Garcia-Lago at 617-355-2500.
Children's Hospital Boston is the nation's leading pediatric medical center, the largest provider of health care to Massachusetts' children, and the primary pediatric teaching hospital of Harvard Medical School. Children's provides pediatric and adolescent health services for patients from birth through age 21. In addition to 325 inpatient beds and comprehensive outpatient programs, it houses the world's largest research enterprise based at a pediatric medical center. More than 500 scientists, including eight members of the National Academy of Sciences, nine members of the Institute of Medicine and 10 members of the Howard Hughes Medical Institute comprise Children's research community. For more information about the hospital visit: www.childrenshospital.org.