This grant seeks to determine the optimal diet composition of the treatment of obesity, as well as the role of exercise and techniques of behavior modification in such therapy. Substantial evidence has now accumulated from uncontrolled experiments that semistarvation ketogenic regimens are effective in the weight reduction phase of obesity treatment. Although both protein and carbohydrate intake during fasting reduce net protein breakdown, the relative efficiency of each to spare lean tissue has been the subject of considerable research and not a little controversy. Since one major goal in the therapy of obesity is to maximize fat loss while minimizing protein loss, it is of considerable interest to determine the relative protein sparing abilities by both classic nitrogen balance as well as kinetic measures of protein and glucose metabolism of low calorie protein only versus a mixed protein-carbohydrate diet. Studies under this grant have been directed towards estimating the protein and glucose dynamics in response to low calorie protein and mixed diets and defining the significant metabolic and clinical differences and characteristics of these diets in the management of obesity. With the increasing prevalence of obesity as a major clinical and public health concern, such research can be anticipated to be helpful in the development of recommendations as to the optimal diet composition in the treatment of obesity.