Impact of Formula Protein Quantity and Source on Infant Metabolism: Serum, Urine and Fecal Metabolomes of a Randomized Controlled Study.

Abstract

Background: Human milk offers significant health benefits for infants; however, when not feasible, infant formula serves as an alternative. The higher protein content in infant formula is thought to contribute to the distinct metabolic profiles observed in formula-fed infants compared to those fed human milk.

Objectives: This study investigates the impact of formula protein quantity and whey protein types on the serum, urine, and fecal metabolomes of infants.

Methods: A secondary analysis was performed on a random subset of 200 well-characterized per-protocol infants who completed a prospective, randomized, double-blind controlled trial. Infants were randomly assigned to one of three groups: standard formula, protein-reduced formula with α-lactalbumin-enriched whey, or protein-reduced formula with casein glycomacropeptide-reduced whey, along with an observational reference group of exclusively human milk-fed infants. Serum, urine, and fecal metabolites were quantified using ¹H NMR spectroscopy at baseline (1-2 months), 4, and 6 months of age. Dietary intake was assessed monthly up to 6 months of age.

Results: Formula protein content and type of whey protein used significantly influenced the amino acid profile and associated catabolic markers in serum and urine but had minimal impact on the fecal metabolome. Reduced protein formulas yielded metabolome profiles closer to those of human milk-fed infants compared to standard formula. Despite these improvements, infants fed human milk still demonstrated enhanced branched-chain amino acid (BCAA) oxidation and a greater capacity to eliminate catabolic waste products from BCAA metabolism over infants consuming protein-reduced formulas.

Conclusions: Comprehensive metabolomics profiling of serum, urine and feces captures molecular-level changes and informs potential strategies for formula optimization. Both the quantity and source of protein significantly influenced the metabolic profiles of formula-fed infants. However, modifications in protein alone cannot fully resolve the metabolic differences between formula-fed and human milk-fed infants, highlighting the complexity of mimicking the human milk feeding-associated metabolic profile.

Clinical trial registration: This study was registered at ClinicalTrials.gov as NCT02410057.