All of the relevant topics that could be included under the title of this chapter
would cover an extraordinary range of biological knowledge; more than is possible
to include in an article of restricted length.
The maintenance of body protein mass depends on the dynamic equilibrium between
the opposing processes of protein synthesis and protein degradation.
Proteins in breast milk and infant formulas are often assumed to be well utilized
by infants and to cover their amino acid requirements.
By definition, mammals are those animals that suckle their young and they comprise
the highest class of vertebrates.
The whole body degradation rates of cytoplasmic transfer RNA (tRNA), ribosomal
RNA (rRNA), and messenger RNA (mRNA) in mammals can be determined noninvasively
using high-performance liquid chromatography, by measuring the urinary
excretion of special modified RNA catabolites (ribonucleosides, nucleobases) which
are excreted virtually quantitatively (1-4).
The definitive international report on protein requirements is the one published by
the WHO in 1985 (1).
The class of compounds called non-protein nitrogen (NPN) is not a homogeneous
group of similar chemicals but rather an operational term for the remainder of nitrogen
in milk and formula once the protein fraction has been removed.
Since analytical data on the different composition of human milk and cow's milk
became available at the beginning of this century, human milk has always been the
gold standard for creation of infant formulas.
A definition of the protein requirement of any population must include consideration
of the purposes for which the requirement is being defined.
The approach most commonly used has been to estimate the intake of protein by
exclusively breast-fed infants who are maintaining satisfactory growth.
Weaning, the period in which non-milk foods are introduced into the diet, is one
of the most critical nutritional events in the life of mammals.
There has been an evolution in the appreciation of the functional roles that amino
acids play in neonatal nutrition over the last 30 years.
Nucleotides are low molecular weight intracellular compounds that play major
roles in physiological and biological functions.,
Inborn errors of metabolism are caused by mutations that alter the functions of
physiologically important proteins.
The relentless catabolism of body protein during chronic disease may kill. Early
investigators presumed that the origins of cachexia lay in the underlying neoplasia
or organism usurping the host's energy stores.