Human milk is a comprehensive source
of nutrition for newborns.
The composition of human milk is
dynamic and evolves with time, imaginably,
to adapt to the nutritional need
of the infants.
The concentration of protein in human
milk follows a temporal pattern
and decreases with progressing stages
Human milk provides unparalleled nutrition
to infants in early stages of life.
Consequently, the WHO/UNICEF, the
American Academy of Pediatrics and
other similar organizations recommend
exclusive breast-feeding for the
first 6 months of life, with the introduction
of complementary food at the age
of 6 months and continuation of
breast-feeding for as long as mutually
agreeable by the mother and the infant
[1, 2]. Human milk is a comprehensive
source of energy, macronutrients as
well as bioactive micronutrients essential
for the growth and development
of an infant, with possible exceptions
of iron and vitamin D . It is also
a very dynamic fluid and may evolve
with advancing stages of lactation to
reflect the nutritional need of the
growing infant. Various nutrients in human
milk display such dynamism, and
indeed protein fraction is one of them.
We recently reviewed 34 publications
and examined data on true protein in
human milk at various lactation stages
from 26 publications to highlight the
evolution of proteins in human milk
during the first year of life . As evident
from figure 1, there is a significant
decrease in true protein in human
milk from the very first week of lactation.
The decline in the concentration
of the protein continues to 6 months
of life, after which it remains relatively
constant. It is also noteworthy that
during the early stages of lactation
there is a high content of whey fraction
in human milk compared to caseins
(approximately 90:10 to 80:20) that
transitions to 60:40 in transition milk
and to 50:50 in mature milk [5, 6]. Additionally,
colostrum protein is rich in
immune and growth factors. Moreover,
there are also multitudes of bioactive
proteins in human milk, such as
lactoferrin, lysozyme, secretory IgA,
haptocorrin, α-lactalbumin, bile saltstimulated
lipase, κ-casein, and
β-casein . Indeed, research over the
past decades has given us insights
into the dynamics of total and true protein
in human milk; however, future
research is required to understand the
dynamics of bioactive proteins with
advancing stages of lactation along
with their contribution of biological activities
at various stages of an infant’s
World Health Organization: Infant and young
child nutrition. Geneva, WHO, 2003.
American Academy of Pediatrics: Breastfeeding
and the use of human milk. Section
on breastfeeding. Pediatrics 2012;129:e827–
Denne SC: Neonatal nutrition. Pediatr Clin
North Am 2015;62:427–438.
Destaillats F, Erdmann P, Thakkar SK,
Lönnerdal B: A developmental perspective of
the contents of total protein and bioactive
proteins in breast milk. In preparation.
Kunz C, Lönnerdal B: Re-evaluation of the
whey protein/casein ratio of human milk.
Acta Paediatr 1992;81:107–112.
Lönnerdal B: Nutritional and physiologic
significance of human milk proteins. Am J
Clin Nutr 2003;77:1537S–1543S.
Lönnerdal B: Bioactive proteins in breast milk.
J Paediatr Child Health 2013;49(suppl 1):1–7.
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