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Energy Expenditure, Protein Oxidation and Body Composition in a Cohort of Very Low Birth Weight Infants

Michela Perrone¹, Camilla Menis^1,2, Pasqua Piemontese¹

¹Neonatal Intensive Care Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, 20122 Milan, Italy.

|November 27, 2021

Insights

Human milk-fed preterm infants have lower protein oxidation and better growth than formula-fed infants, despite similar resting energy expenditure (REE). This suggests human milk promotes anabolic growth in very low birth weight infants (VLBWI).

Area of Science:

Neonatal nutrition
Pediatric metabolism
Growth and development

Background:

Nutritional management of preterm infants is crucial to prevent extrauterine growth restriction (EUGR).
Accurate estimation of energy requirements is challenging, as predictive formulas for resting energy expenditure (REE) are imprecise.
Understanding energy expenditure and protein metabolism is key for optimizing growth in very low birth weight infants (VLBWI).

Purpose of the Study:

To evaluate resting energy expenditure (REE) and protein oxidation (Ox) in VLBWI.
To assess the association between feeding method (human milk vs. formula) and body composition at term corrected age.

Main Methods:

Indirect calorimetry and body composition analysis (air displacement plethysmography) were performed in stable VLBWI at term corrected age.
Urinary nitrogen was measured to calculate protein oxidation (Ox).
Infants were categorized into prevalent human milk (HMF) or prevalent formula diet (PFF) groups.

Main Results:

No significant differences in REE were observed between HMF and PFF groups (59.69 ± 9.8 vs. 59.27 ± 13.15 kcal/kg/day).
HMF infants exhibited significantly lower protein oxidation (1.7 ± 0.92 g/kg/day) compared to PFF infants (2.8 ± 1.65 g/kg/day, p < 0.01).
HMF infants demonstrated higher fat-free mass (2.05 ± 0.26 kg) than PFF infants (1.82 ± 0.35 kg, p < 0.01).

Conclusions:

Resting energy expenditure (REE) is comparable between preterm infants fed predominantly human milk or formula.
Prevalent human milk feeding is associated with lower protein oxidation and enhanced fat-free mass accretion, indicating improved growth quality.
Human milk may support anabolism and lean body mass deposition more effectively in VLBWI.

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Abstract:

The nutritional management of preterm infants is a critical point of care, especially because of the increased risk of developing extrauterine growth restriction (EUGR), which is associated with worsened health outcomes. Energy requirements in preterm infants are simply estimated, so the measurement of resting energy expenditure (REE) should be a key point in the nutritional evaluation of preterm infants. Although predictive formulae are available, it is well known that they are imprecise. The aim of our study was the evaluation of REE and protein oxidation (Ox) in very low birth weight infants (VLBWI) and the association with the mode of feeding and with body composition at term corrected age.

Methods:

Indirect calorimetry and body composition were performed at term corrected age in stable very low birth weight infants. Urinary nitrogen was measured in spot urine samples to calculate Ox. Infants were categorized as prevalent human milk (HMF) or prevalent formula diet (PFF).

Results:

Fifty VLBWI (HMF: 23, PFF: 27) were evaluated at 36.48 ± 0.85 post-conceptional weeks. No significant differences were found in basic characteristics or nutritional intake in the groups at birth and at the assessment. No differences were found in the REE of HMF vs. PFF (59.69 ± 9.8 kcal/kg/day vs. 59.27 ± 13.15 kcal/kg/day, respectively). We found statistical differences in the protein-Ox of HMF vs. PFF (1.7 ± 0.92 g/kg/day vs. 2.8 ± 1.65 g/kg/day, respectively, p < 0.01), and HMF infants had a higher fat-free mass (kg) than PFF infants (2.05 ± 0.26 kg vs. 1.82 ± 0.35 kg, respectively, p < 0.01), measured with air displacement plethysmography.

Conclusion:

REE is similar in infants with a prevalent human milk diet and in infants fed with formula. The HMF infants showed a lower oxidation rate of proteins for energy purposes and a better quality of growth. A greater amount of protein in HMF is probably used for anabolism and fat-free mass deposition. Further studies are needed to confirm our hypothesis.

Keywords:

body composition indirect calorimetry preterm infants resting energy expenditure substrate oxidation

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