Early lactation breast milk protein and lactose as independent predictors of infant regurgitation: A prospective cohort study

OBJECTIVES: To examine whether breast milk (BM) macronutrient composition in the first 2 weeks postpartum is associated with subsequent infant regurgitation (IR) risk, independent of maternal dietary intake. METHODS: In this prospective cohort study (Beijing, China), 78 mother-infant dyads were followed for 5 months. BM samples were collected at 1-2 weeks, 1, 2, and 5 months postpartum. IR was diagnosed using Rome IV criteria. Macronutrient composition (protein, fat, lactose) was analyzed using standardized methods. Maternal diet was assessed via a validated food frequency questionnaire. Multivariable logistic regression adjusted for maternal (body mass index, gestational age) and infant (birth weight, gender) characteristics. RESULTS: IR incidence peaked at 1 month (61.5%) and declined thereafter. Compared with controls, infants who developed IR at 1-2 months were exposed to lower protein and higher lactose concentrations in BM collected at 1-2 weeks (p < 0.05 for both). Maternal dietary intake was not associated with BM macronutrient composition. In adjusted models, lower early BM protein (odds ratio [OR] 0.090; 95% confidence interval [CI] 0.012-0.670) and higher lactose (OR 2.571; 95% CI 1.039-6.363) were associated with increased IR risk at 1 month. CONCLUSIONS: Early BM composition may be associated with subsequent IR risk, independent of maternal diet. Protein and lactose levels in early lactation may serve as potential markers for identifying infants at risk. These findings suggest early lactation as a sensitive period linking maternal physiology to infant gastrointestinal outcomes.