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close this bookProtein-Energy Interactions (IDECG, 1991, 437 p.)
close this folderThe metabolic basis of amino acid requirements
View the document(introduction...)
View the documentAbstract
View the document1. Introduction: The nature of the problem
View the document2. Nutrient requirement models
View the document3. The Millward & Rivers requirement model: Qualitative aspects
Open this folder and view contents4. The variable extrinsic component of the maintenance requirement
View the document5. The anabolic drive
View the document6. Hormonal components of the anabolic drive
View the document7. Protein requirements: Formal statement
Open this folder and view contents8. The issue of protein quality
View the document9. Stable isotope studies
View the document10. Practical experience of biological values of dietary protein
View the document11. Urea salvage
View the document12. Indispensable amino acid requirements for the anabolic drive
View the document13. Conclusions
View the documentReferences

7. Protein requirements: Formal statement

From this we can construct a protein requirement statement, as in Table 2. In our original paper we said that the requirement will be equal to G (growth) + Lo (ONL) + Lr (the regulatory oxidative loss) and argued that, since the magnitude of Lr varies with the intake, we could only define an operative value for Lr and the requirement. Since balance can be achieved over a range of intakes, we need to be able to make judgements about the value to the organism of any particular level of oxidative loss. This is the point at which the importance of the anabolic drive can be recognised, since it allows definition of an optimal requirement level (Ropt), as distinct from the minimum level (Rmin) which, in practice, has been the previous objective.

Table 2. Components of the minimum and optimum protein requirement

Functional needs (intrinsic)

Regulatory losses (extrinsic)

growth (G)

ONL (Lo)

anabolic drive (Lr optimum)

oxidative losses (Lr operative)

minimum requirement:
minimum intake for N balance after adaptation
Rmin = G + Lo + Lr min

optimum requirement:
intake for N balance after adaptation and desired functional response
Ropt = G + Lo + Lr opt