Protein requirements of adults.

Abstract

Abstract 1.1. Nitrogen balance studies on twenty-six adults in apparent good health were made using a low protein diet, devoid of animal protein, in which approximately 50 per cent of the protein was supplied by white bread, 12 per cent by other cereals, 30 per cent by vegetables, and 8 per cent by fruit. Adequate calories to maintain caloric equilibrium were supplied by sugars, starch, and fats. It was found that the nitrogen requirement is more closely related to surface area (basal caloric expenditure) than to body weight. The requirement for maintaining nitrogen balance was approximately 2.9 Gm. of nitrogen (18 Gm. conventional protein) per square meter of body surface. A man weighing 70 kilograms would thus require between 30 and 40 Gm. of protein, depending upon height. 2.2. On the same diet with one-third of the protein replaced by meat, the requirement appears to be about 2.4 Gm. nitrogen (15 Gm. conventional protein) per square meter. Protein requirement is thus about 17 per cent less on this diet than on the all-vegetable diet. 3.3. Data on digestibility and biologic value were determined and the equal importance of these two measurements for evaluating the nutritional value of a protein is emphasized. High quality proteins are more efficient, but less efficient proteins may serve equally well, provided enough can be fed to cover the requirement considering the specific digestibility and biologic value. 4.4. The biologic value of the low protein all-vegetable diet used in these studies was increased from 72.5 to 80.4 by replacing one-third of the protein with meat. The digestibility of the two diets was essentially the same. 5.5. There was no measurable objective change in the physical condition of any of the individuals throughout these studies. Some complained of undue postprandial hunger and fatigue on the low protein all-vegetable diets. These complaints were not present on high protein diets. 6.6. There were no significant changes in hemoglobin, hematocrit, or plasma volume. Total protein, plasma albumin, and plasma globulin tended to decrease on the low protein all-vegetable diet when fed at a level low enough to produce negative nitrogen balance. The replacement of one-third of the protein in this diet with meat resulted in a prompt increase in the globulin fraction. 7.7. It is most unlikely that protein deficiency will develop in apparently healthy adults on a diet in which cereals and vegetables supply adequate calories. 8.8. Considering the experimental data presented in this study, the National Research Council's daily recommended allowance of 70 Gm. of protein for an adult weighing 70 kilograms is most generous and could, if necessary, be reduced to 50 Gm. and still provide approximately 30 per cent margin above requirement. 9.9. It should be emphasized that the experimental data and the conclusions of this paper apply to adults in apparent good health and do not consider protein requirements in growth, pregnancy, lactation, or disease.