MAINTENANCE VALUES FOR THE PROTEINS OF MILK, MEAT, BREAD AND MILK, AND SOY BEAN CURD

The recent exhaustive review by Mitchell (1) of the literature relating to the nutritive value of proteins renders superfluous any extensive discussion of this topic by us.Consequently we shall review very briefly only such papers as have to do with the utilization by the human subject of the foods under immediate consideration.Beyond doubt the search for an absolute biological constant in protein metabolism is a vain one; any so called biological minimum is such only for a given set of conditions.The influence of the energy value of the diet upon the efficiency with which its protein is utilized has long been recognized.Neumann's (2) 40 day experiment upon himself is an excellent illustration.Living exclusively upon rye bread, cane sugar, and water, he found in a 5 day period on bread alone, with 42.3 calories per kilo and total nitrogen intake 9.9 gm.daily, a negative nitrogen balance; in the next 5 day period the addition of 300 gm. of cane sugar (making 63.8 calories per kilo) changed this to a positive balance; and in the succeeding 8 day period with 500 gm. of cane sugar (making 77.1 calories per kilo) there was storage of 1.6 gm. of nitrogen daily; in other words, increasing the calories 55 per cent changed the nitrogen situation from a loss equal to 20 per cent of the intake to a storage equal to 17 per cent.Cathcart (3) has lately called attention to the difference of opinion existing in regard to the influence of muscular work upon the nitrogen output, and cites about twice as many investigators 847This is an Open Access article under the CC BY license.