To determine the effects of length of gestation and sex on infant body composition, air displacement plethysmography was performed in forty-six full-term neonates at 3 d of life and during the week prior to hospital discharge in 180 preterm neonates. Fat mass, as a percentage of body weight, was higher in preterm than in term infants (13·4 (sd 4·2) v. 10·1 (sd 3·7) %, respectively; P= 0·001). The absolute amount of fat mass did not differ between preterm and full-term newborns (323 (sd 126) v. 335 (sd 138) g; P= 0·58), whereas lean body mass was lower in preterm than in term infants (2055 (sd 280) v. 2937 (sd 259) g, respectively; P< 0·001). Among full-term infants, fat mass was higher in females than in males (11·1 (sd 3·7) v. 9·0 (sd 3·3) %, respectively; P= 0·047), whereas we did not observe any sex difference in preterm infants (13·5 (sd 4·1) v. 13·4 (sd 4·3) %; P= 0·89). Our data suggest that by the time they are discharged from hospital: (1) preterm infants have a higher percentage of body fat than term neonates and (2) this is presumably due to a lesser accretion in lean body mass in the first few weeks of extra-uterine life, particularly in boys.

Bovine and human k-caseinoglycopeptides, two antithrombotic peptides derived from the corresponding k-caseins, were detected in physiologically active concentrations in the plasma of 5-d-old newborn infants after ingestion of cow's-milk-based formula or human milk respectively. It is suggested that these two bioactive peptides are released from milk proteins during digestion.