The Estimation of Relative Nutrient Intake and Nutritional Status by Biochemical Methods: Proteins

Abstract

When the intake of dietary proteins is reduced, some biochemical changes occur in the body, which may be grossly grouped into three stages of development: (1) decrease in the metabolic expenditure of body proteins, (2) decrease in the “protein reserves,” and (3) decrease in some protein moieties with key metabolic function. Biochemical methods applicable at these different stages, which will give information on the protein intake and nutritional status, are suggested. The urinary excretion of urea under fasting conditions, particularly its ratio to creatinine, is proposed as an informative test at stage 1. The preliminary evidence presented points to its usefulness as a simple way to estimate levels of “utilizable protein” intake. Urinary creatinine per unit of time per centimeter of height is discussed as a practical indicator of muscle mass development during stage 2. Alterations in total plasma protein and its electrophoretic fractions, as well as of some enzymes of plasma and tissues (stage 3), can be detected biochemically but seem to appear only at the last stage of protein deficiency when the condition is severe enough to be clinically evident.