Metabolic differences between AGA- and SGA-infants of very low birthweight. II. Relationship to protein intake.

The metabolic response to different levels of human milk protein intake was studied in 23 appropriate (AGA) and 19 small for gestational age (SGA) infants of very low birthweight (VLBW) on the eighth day of life. The infants received from birth, either fresh preterm human milk or human milk fortified with lyophilized human milk (6 g per 100 ml). Thus, the protein intake ranged from 1.98 to 3.28 g/kg/d in the AGA- and from 1.94 to 3.34 g/kg/d in the SGA-infants. Alpha-amino-nitrogen and bile acid concentrations in serum and total- as well as alpha-amino-nitrogen excretion in the urine were measured. When the protein intake was less than 2.5 g/kg/d no differences between the groups could be found in any of the parameters directly related to nitrogen metabolism, but a significantly higher concentration of bile acids in serum was found in the SGA-infants. On protein intakes of more than 2.5 g/kg/d the SGA-infants responded with higher alpha-amino-nitrogen as well as total bile acids concentrations in the serum and also with higher excretions of total- as well as alpha-amino-nitrogen in the urine when compared to the AGA-infants. The differences between the groups became more pronounced with an increasing protein intake. The data suggest that on the eighth day of life SGA-infants are more sensitive to an excessive protein intake than AGA-infants. Hepatocellular dysfunctions as a result of intrauterine growth retardation seems to be an important factor in this special metabolic situation. Bile acid concentration in the serum can be used as a good marker to detect this. The observed differences in the metabolic capacity to handle protein between AGA- and SGA-infants on the eighth day of life have to be considered in the nutritional management of VLBW-infants.