Obesity in affluent countries continues to be a serious problem. When one runs an Obesity Clinic there appears to be an unending series of patients who need help. Our understanding of weight control has been advanced not only by the studies of obese patients but also by our investigation of the problems of weight gain in young women with anorexia nervosa. Just as among obese patients there is the group of 'efficient metabolizers' who can maintain their excessive weight with a calorie intake occasion- ally as low as 600 kcal per day, so we have demonstrated that among anorexic women there are...