Influence of Protein and Amino Acid Supply on Tissue Function and Metabolism

Abstract

In a Symposium on the Pathophysiological Basis of Intensive Therapy, it is important to recognize the need to maintain the patient in a good nutritional state. In the past, it has not been sufficiently recognized that disease can cause poor nutritional status in two ways. First, there is the well-known loss of appetite in some diseases, so that less than an adequate food intake is eaten. This will be dealt with later in the symposium. Second, it is less well recognized that certain diseases can increase the requirements for nutrients. For example, Table 1 contains an analysis of the factors involved in the protein requirements of man and lists some of the diseases which cause increases in one or more of these components (Munro, 1964). Protein requirements are assessed by measuring the obligatory losses of nitrogen that occur in the feces and in the urine and from the skin when a

Table 1. Minimum N output of man on a protein free diet and increased N losses caused by disease

Channel of N loss	Normal daily N loss on protein-free diet	Diseases increasing N loss
Feces	0.6 gm	Gastrointestinal diseases (e.g. ulcerative colitis, up to 6 gm/day)
Urine	0.7 gm	Increased metabolism (e.g. 50 % increase in hyperthyroidism and in renal failure)
Cutaneous	0.7 gm	Skin diseases (e.g. burns exudate of 10–50 gm protein/day)

subject is given a protein-free diet. It is assumed that the diet must provide sufficient protein to balance these obligatory losses (see Munro, 1964, for a further discussion of this). Diseases are known which can increase each of these channels of obligatory nitrogen loss, and thus increase the amount of dietary protein needed to replace these losses. For example, kidney damage with renal failure causes not only a loss of protein in the urine, which has to be replaced from the diet, but it also increases the urinary output of non-protein nitrogen when these patients are given a protein-free diet; thus the increased need for dietary protein in such cases can be quite considerable. This increased protein requirement in renal damage cases must therefore be considered when recommending a low intake of protein for uremic subjects with kidney disease.