Standard treatment for obesity, based on a law of physics, assumes that all calories are alike, and that to lose weight one must simply “eat less and move more.” However, this prescription rarely works over the long term. According to the Carbohydrate-Insulin Model of obesity, the metabolic condition of fat cells plays a key role in determining body weight. High intakes of processed carbohydrate raise insulin levels and program fat cells to store too many calories, leaving too few for the rest of the body. Consequently, hunger increases, and metabolic rate slows in the body’s attempt to conserve energy. From this perspective, calorie-restricted, low-fat diets amount to symptomatic treatment, destined to fail for most people. Instead, a dietary strategy aiming to lower insulin secretion promises to increase the effectiveness of long-term weight management and chronic disease prevention.

David S. Ludwig, M.D., Ph.D., is an endocrinologist and researcher at Boston Children’s Hospital, professor of pediatrics at Harvard Medical School and professor of nutrition at Harvard School of Public Health. For more than 25 years, Dr. Ludwig has studied the effects of dietary composition on metabolism, body weight and risk for chronic disease—with a special focus on low glycemic index, low carbohydrate and ketogenic diets. Described as an “obesity warrior” by Time magazine, Dr. Ludwig has fought for fundamental policy changes to improve the food environment. He has authored more than 200 scientific articles and presently serves as an editor at the American Journal of Clinical Nutrition and The BMJ. Dr. Ludwig is author of the number-one New York Times bestseller Always Hungry? Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently.