Protein & Amino Acids - Ask the Dietitian®
The processes of protein synthesis and possibly of breakdown(turnover) require sources of dietary energy and are thus sensitiveto energy deprivation. Consequently, the energy balance of the bodybecomes an important factor in determining nitrogen balance andinfluences the utilization of dietary protein.
Protein needs for the athlete or body builder may be higher
The magnitude of the basal energy needs and of the total amountof protein turned over in a day are both related to active tissue mass(). Moreover, in young animals and growing children bothrates per unit of active mass are increased compared with thoseobserved in adults (). Nevertheless, as discussed in the nextsection, it has not proved possible to establish a constant numericalrelationship, covering all age ranges, between BMR and eitherprotein requirement or obligatory nitrogen loss, although such arelationship has been assumed by previous committees ().
However, the evidence on which these observations were basedis of limited value. Firstly, most habitual diets derive 10–14% oftheir energy from protein. Thus, when energy intake rises, so doesprotein intake and also intakes of many of the nutrients associatedwith protein in foods, such as the B-group vitamins and traceelements. Secondly, it is obvious that many environmental factorswill influence any selected measure of health. Populations thatcharacteristically have higher levels of protein intake tend to liveunder healthier conditions, whereas those with habitually lowerintakes are much more likely to be exposed to parasitic andinfectious disease. These confounding factors make it extremelydifficult to attempt to draw causal relationships. Thirdly, there aremany different measures of health and wellbeing; the criteria aretherefore complex and cannot easily be used to set physiologicalrequirements for protein.