For years it has been assumed that the caloric needs of man were well understood. This assumption was based on the work of Rubner, Benedict, Lusk, Du Bois and others who with calorimeters diligently gathered the information needed for the calculation of caloric needs of both individuals and groups. In the recent war opportunities developed for studying large groups of men over extended periods. Individual experiments in the past had often been done under circumstances that left doubts as to the rigor with which the given diet was observed. The war, however, created situations in which whole groups became completely dependent on strictly rationed supplies. Studies made under these conditions have corroborated observations previously made by slow, painstaking calorimetric studies on individuals. Kraut and Muller1 have related the caloric intake of workers to their industrial output. Their observations confirm some accepted beliefs about the human body. The body is