Protein use and weight-gain quality in very-low-birth-weight preterm infants fed human milk or formula

Nutritional management of preterm infants aims to approximate the tissue growth and body composition of a fetus of the same postmenstrual age. The adequacy of the quality of protein supply can influence the rate and the relative quality of weight gain. We investigated the protein balance according to feeding regimen and the association between human milk feeding and fat-free mass content at the term-corrected age in very-low-birth-weight preterm infants. A prospective observational study was conducted. Inclusion criteria were as follows: healthy infants, gestational age ≤32 wk, birth weight <1500 g, stable clinical conditions, and feeding by mouth with human milk or formula at discharge. Infants were enrolled at hospital discharge. At enrollment, macronutrient intakes and protein balance were determined. Anthropometric measurements and body composition were also assessed. The nutritional composition of human milk was calculated by infrared spectroscopy. The protein balance was determined according to the nitrogen balance standard method. Body composition was assessed by an air-displacement plethysmography system. At the term-corrected age, anthropometry and body composition assessments were repeated. Seventeen preterm infants fed fortified human milk and 15 preterm infants fed formula were enrolled. At discharge, despite similar macronutrient intakes, infants fed fortified human milk showed a higher nitrogen balance (expressed as mg · kg⁻¹ · d⁻¹) compared with preterm formula-fed infants (mean ± SD: 488.3 ± 75 compared with 409.8 ± 85 mg · kg⁻¹ · d⁻¹, P = 0.009). At term-corrected age, growth was similar in the 2 groups, whereas fortified human milk–fed infants showed a higher percentage of fat-free mass (85.1% ± 2.8% compared with 80.8% ± 3.2%, P = 0.002). Moreover, at multiple linear regression, fat-free mass content was independently associated with being fed human milk (R² = 0.93, P < 0.0001). Our findings suggest that human milk feeding is associated with early fat-free mass deposition in healthy and stable preterm infants. This trial was registered at www.clinicaltrials.gov as NCT03013374.