Stable isotope tracers and the determination of fuel fluxes in newborn infants.

After birth, newborns adapt from the in utero situation of a continuous fuel supply to the postnatal situation of feeding and fasting periods. In order to maintain adequate fluxes of energetic substrates to their various organs and tissues, neonates must rapidly activate the release of glucose, free fatty acids and ketone bodies into the blood stream. This review will summarize some of the techniques and results available today regarding the in vivo kinetics of an energetic substrate in early postnatal life: the rate of production of this substrate, the overall rate of its uptake by the tissues, its rate of oxidation and contribution to the total caloric demand, the rate of conversion of a precursor into this substrate.