Assessment of protein requirements by nitrogen balance

The earliest estimates of protein requirements, such as those of Smith (1863) and Pavy (1874) who recommended about 125 g per day for the average working man, were based on studies of the diets of individuals or of groups of subjects who were considered to be healthy and leading normal active lives. Such estimates were simply a reflection of the dietary habits of those under study, but helped to establish minimum standards of feeding in institutions. About the turn of the century, similar recommendations ranging from 118 to 150 g were made by Voit (1881), Atwater (1895) and Rubner (1903) (Fig. 1), and these came to be vigorously defended as representing not merely feeding standards but as irreducible minima below which a proper state of health and vigour could not be maintained.