How age factors affect the requirement of protein?
Age: Protein in excess of maintenance needs is required, when a new tissue is being fornled. Certain age periods, when growth is rapid, require more dietary protein than other periods. Age differences in protein turnover, as well as, protein synthesis explain some of the effects of age on protein needs. Premature infants (those born before their 10 lunar month gestation time) growing at a very rapid rate require between 2.5 to 5 g protein kg/day if they are to survive. Studies of full term infants have indicated that a protein intake of 2.0 to 2.5 g kg/day resulted in a satisfactory weight gain and that further increases in protein intake did not measurably improve growth. Older infants and children, whose growth rate is not as rapid as the premature or new born infant, require considerably less protein (1.25 g/kg/day). As growth rate increases during adolescence, the protein needs increase. Again, this can be related to the demands for dietary amino acids .to support the growth process. As the human completes his growth, the need for protein decreases until it arrives at a level which is called the 'maintenance level'. It is at this level that the concept of body protein replacement by dietary protein applies.
During the growth period, it is very difficult to separate the requirements for maintenance from those of growth. The impulse for growth is so strong that it will occur in many instances at the expense of the maintenance of body tissues. For example, malnourished children will continue to grow taller even though their muscles, as well as, other tissues show evidence of wastage due to dietary protein deficiency. Growth carries with it not only a total nitrogen requirement but also a particular amino acid requirement. Maintenance, on the other hand, appears to have only a total protein requirement. The adult can make a number of short-term adjustments in his protein metabolism that can compensate for possible inequities of imbalances in amino acid intake as long as the total protein requirement is met. The young growing animal is not that flexible. The essential amino acid requirements are age dependent. Although histidine can be synthesized in sufficient quantity by the adult to meet maintenance needs, yet it is no1 synthesized in great enough amounts to support growth or tissue repair. Thus, histidine is an essential amino acid for the infant, growing child and injured adult. This is due to the nature of the growth and repair processes.