Fat and mineral metabolic balance studies were performed in 25 normal very low-birth-weight infants (< or = 1500 g at birth) fed either pooled pasteurized human milk supplemented with calcium, phosphorus and magnesium, or a preterm formula. Calcium, phosphorus and magnesium intake were similar in both groups and averaged 100 mg/kg/day, 72 mg/kg/day and 8 mg/kg/day, respectively. Calcium and phosphorus retention was higher in the subjects fed fortified human milk than in those receiving a preterm formula (65 +/- 14 and 62 +/- 9 mg/kg/day versus 55 +/- 12 and 47 +/- 7 mg/kg/day respectively). The difference was only significant for phosphorus. Magnesium retention was similar in the two groups and averaged 3 mg/kg/day. Fat intake and absorption was significantly higher in the preterm formula fed group than in the one fed fortified human milk (5.5 +/- 0.4 g/kg/day and 88 +/- 4% versus 4.2 +/- 1 g/kg/day, 79 +/- 6% respectively). Assessment of the whole body bone mineral content by dual energy X-ray absorptiometry was performed at 3 and 6 months of age in another group of 25 low-birth-weight infants fed either fortified human milk or a preterm formula. Whole body bone mineral content (BMCt) was low (43.3 +/- 30.8 g of hydroxyapatite) at 3 months of age (theoretical term) compared to normal full-term newborns at birth. There was no significant influence of the diet. At 6 months of age, BMCt reached 168.6 +/- 36.6 g, a value similar to that of full-term newborns, with no significant difference between the two regimen groups.(ABSTRACT TRUNCATED AT 250 WORDS)