Weight Gain from Simple Overeating. II. Serum Lipids and Blood Volume 1

Many questions about the processes and events in the reduction of obesity in man are still obscure or even unexplored, in spite of a very large number of clinical and experimental studies. The reverse situation, the production of obesity in man, has had practically no detailed attention except for scattered clinical observations in rare pathological states. That obesity develops whenever a positive calorie balance is maintained over a long period of time, is axiomatic but not very informative. Positive calorie balance may, of course, reflect increased calorie intake, decreased output, or both, and the details of metabolism and physiological adjustments are not necessarily the same in these several conditions. It would be expected, in fact, that the effects of a sharp reduction in physical activity without change in the diet must be quite different from those of increased diet and no alteration in activity. In the natural (spontaneous) development of obesity in organically healthy man which is so common in our modern society, alterations both in calorie intake and output are probably involved and, in addition, the character of the diet is often changed. What factors, then, are responsible for the various morphological, biochemical, and physiological differences between the person before and after the development of obesity ? Animal experiments on these questions are useful, of course, but the relationships in the production of obesity in the rat or other laboratory animals are not quantitatively transferable to the human situation. We have elected to begin the study of these questions in man by the experimental production of obesity by simple overfeeding without substantial change in physical activity, using for this purpose a diet in which the calorie increase is provided one-third by fat and two-thirds by