Define Protein Requirement at Different Stages of Life Cycle?
Methods of Estimating and Assessing Protein Requirements at Different Stages of Life Cycle
In this section, we are going to deal with the methods that are used to estimate protein requirements, as well as, the factors which affect it. Let's read and find out first what we mean by protein requirement and its significance. Human protein and amino acid requirements have been studied for well over 100 years using a variety of techniques. Nutrition scientists have collected data on the quantity of protein foods consumed in health, growth and weight gain of various populations. The assumption was made that whatever healthy people ale was probably what kept them, healthy and should, therefore, be used as a standard of comparison for other diets. These standards with respect to protein were invariably high for populations having an abundance of meat, milk, poulhy and fish in their diets. Voit and Atwater around the torn of the 20th century, found intakes of 11 8 and 125 g protein/ day, respectively for an adult woman and man. As nutrition developed as a science, more accurate methods for assessing nutrient needs were developed. Among these methods were those for assessing the intakes and excretion of nitrogen compounds. The Kjeldahl method, about which we learnt above, and other methods for determining the nitrogellous end products of metabolism were devised.
These methods made possible the development of the concepts which today's scientists use to determine the nutrient requirements of humans, as well as, other species. In protein nutrition, it was realized that the body consists of two pools of protein: one which has a short half life and which must be constantly renewed and one which is slowly broken down and rebuilt. If one assumes that over a short period of time, the pool having the long half life contributes almost nothing to the nitrogenous metabolic end products and then a measure of the amount of nitrogen excreted will reflect only the turnover of the short lived proteins. These proteins have to be replaced by proteins newly synthesized from the amino acids provided by the diet. Hence, the term protein requirement means that 'amount of protein which must be consumed to provide the amino acids for the synthesis of those body proteins irreversibly categorized in the course of the body metabolism'. The intake of nitrogen from protein must be sufficient to balance that excreted; this basic concept is called nitrogen balance. This concept is useful in understanding the minimal need for protein in the diet.