Cell Metab. 11, 206–212 (2010)

Mother's milk fires up a heat-generating metabolic pathway in newborn mice.

Newborns have to rapidly adjust to the comparatively chilly environment outside the womb. Francesc Villarroya of the University of Barcelona in Spain and his colleagues found that expression of a metabolic regulator gene called Fgf21 increases immediately after birth. However, this increase was seen only when pups were allowed to suckle or were given a lipid-rich emulsion to drink. Pups fed a glucose solution — a diet similar to what they would have received in utero — did not activate Fgf21.

When the FGF21 protein was injected into newborns that were not allowed to nurse, genes associated with heat generation in brown fat, a tissue specialized in heat production, were activated in the pups.