The composition of human milk is the biologic norm for infant nutrition. Human milk also
contains many hundreds to thousands of distinct bioactive molecules that protect against infection
and inflammation and contribute to immune maturation, organ development, and healthy
Exclusive human milk feeding for the first 6 months of life, with continued breastfeeding for
1 to 2 years of life or longer, is recognized as the normative standard for infant feeding.1,2
Human milk is uniquely suited to the human infant, both in its nutritional composition and
in the non-nutritive bioactive factors that promote survival and healthy development.3 Here,
we briefly review the nutritional composition of human milk and provide an overview of its
varied bioactive factors, which include cells, anti-infectious and anti-inflammatory agents,
growth factors, and prebiotics. Unlike infant formula, which is standardized within a very
narrow range of composition, human milk composition is dynamic, and varies within a