In the 1890s the USDA recommended over 110 g dietary protein per day for working men. This was based on Liebig's idea that protein was the source of muscular energy and the observation that protein consumption was higher in the more successful (i.e., affluent) social groups or nations than elsewhere. Chittenden's demonstration of physical energy being maintained on one-half this level of intake then led to reassessment of these standards, and attention was transferred to the discovery of trace nutrients and their practical significance. In the 1950s and 1960s protein again received priority attention. The "World Protein Gap" was considered the major cause of infant mortality and retarded development in the Third World but a problem that could be solved by the application of sophisticated technology. It then appeared that such technology was in general inapplicable to the real-life situation of more primitive communities. It was also found that a more equitable supply of ordinary foods could supply adequate protein, provided that, in the case of infants, attention was paid to their not being too bulky to allow adequate energy intake.