Background: Very preterm (VPT) infants experience poor postnatal growth relative to intrauterine growth rates. Despite poor growth VPT infants at term equivalent age have increased %body fat (%fat) compared with infants born at term. The aim of this study was to identify nutritional and other clinical predictors of infant body composition (%fat, fat mass (FM) and lean mass (LM)) in VPT infants during their hospital stay.
Methods: Daily intakes of protein, carbohydrate, lipid and energy were recorded from birth to 34weeks postmenstrual age (PMA) in 50 infants born <32weeks. All infants had more than 21 days of nutritional data available. Clinical illness variables and anthropometric data were also collected. Body composition was assessed at 34-37weeks PMA age using the PEA POD Infant Body Composition System. Multiple regression analysis was used to identify independent predictors of body composition (%fat, FM or LM).
Results: Birthweight, birthweight z-score and PMA were strong positive predictors of infant lean mass. After adjustment for these factors, the strongest nutrient predictors of lean mass were protein:carbohydrate ratios at multiple postnatal age points. Postnatal age and PMA were the strongest predictors of infant adiposity (%fat or FM). When postnatal age and PMA were accounted for, energy, protein and carbohydrate intakes were negatively associated with FM and %fat.
Conclusions: If growth of lean mass is to be improved, it may be necessary to reduce carbohydrate intakes in addition to increasing protein intakes. In this cohort of VPT infants, a higher intake of energy, protein and carbohydrate was associated with a lower fat mass at 34-37 weeks PMA. We speculate that fat accumulation is triggered at birth and by exposure to low macronutrient intake, both representing a protective response to reduced nutrient availability.