Effects of Infant Formula Type on Early Childhood Growth Outcomes: A Retrospective Cohort Study.

Objective: This study examines the effects of non-standard (lactose-reduced, hydrolyzed), cow-milk-based infant formulas on early childhood growth outcomes compared to standard formulas and breastfeeding. Methods: This retrospective cohort study included full-term infants with a birth weight >2500 g. Exposure and control data, including the type of infant formula [non-standard vs. standard] and breastfeeding status, were obtained at 2-month well visits. Growth outcomes (weight-for-age, length-for-age, BMI (Body Mass Index), and weight-for-length z-scores] were calculated using WHO (World Health Organization) growth standards at 1- and 2-year well visits. Generalized linear mixed models were used to evaluate associations between formula type and growth outcomes, adjusting for maternal, infant, and socioeconomic factors. Results: A total of 5515 infants were included in the final analysis. Feeding practices included exclusive breastfeeding (35%), standard formula (42%), and non-standard formula (23%). Infants fed non-standard formulas had significantly higher weight-for-age, BMI, and weight-for-length z-scores at 12 months than those fed standard formulas, and after controlling for other covariates, weight-for-age and BMI z-scores remained significantly higher in the non-standard formula infants. At 24 months, only weight-for-age z-scores remained significantly higher for non-standard formula users compared to standard formula users. Both non-standard and standard formula groups showed significantly higher weight-for-age, BMI, weight-for-length, and length-for-age z-scores compared to breastfed infants at 12 and 24 months. Conclusions: Non-standard infant formula may have a differential effect on growth during the first year of life compared to standard infant formula and breastfeeding. Future research should explore the long-term health effects of non-standard infant formula use and the risk of obesity.