Methods: In this prospective observational study preterm infants born with a birth weight <1500 g and a gestational age <32 weeks will be recruited at term corrected for prematurity at the neonatal outpatient clinic. Infants will be stratified according their source of milk intake (breast milk, formula and mixed feeding) and their introduction of solid foods (early complementary feeding group: <17th week of life corrected for prematurity, late complementary feeding group: ≥17th week of life corrected for prematurity).