Feeding Practices and Infant Growth: Quantifying the Effects of Breastfeeding Termination and Complementary Food Introduction on BMI z -Score Growth Velocity through Growth Curve Models

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Abstract
Background: Infant feeding practices are a focus of early obesity prevention. We tested whether infant growth velocity increased after breastfeeding termination and complementary food introduction. Methods: Our secondary analysis included a sample of 547 mother-infant dyads from a longitudinal randomized controlled trial conducted in Michigan and Colorado. Infant anthropometrics at birth, baseline, and 6- and 12-month follow-up were standardized to BMI-for-age z-score (ZBMI) according to World Health Organization (WHO) growth charts. We used growth curve models with time-varying predictors to quantify effects of breastfeeding termination and timing of complementary food introduction on growth velocity. Results: Median breastfeeding duration was 2.0 months [confidence interval (CI) = 2.0–2.5]; median introduction of complementary foods occurred at 3.0 months (CI = 2.8–3.2). Breastfed infants not yet introduced to complementary foods had an average ZBMI growth velocity of 0.050 (CI = −0.013 to 0.113) z-score units per month [zpm], not significantly faster than WHO growth trajectory (p = 0.118) defined as 0 zpm. Breastfeeding termination had negligible effect on ZBMI growth velocity (γ11 = 0.001, CI = −0.027 to 0.030, p = 0.927). Introduction of complementary foods increased ZBMI growth velocity relative to an average child in the sample, but not significantly (γ12 = 0.033, CI = −0.034 to 0.100, p = 0.334). Growth velocities for infants receiving complementary foods both before and after breastfeeding termination were significantly faster than the WHO growth trajectory (0.083 zpm, CI = 0.052–0.114, and 0.084 zpm, CI = 0.064–0.105, respectively, p's < 0.001). Conclusions: Average postcomplementary food introduction growth velocity was significantly higher than WHO growth trajectory, but did not differ from the sample's initial average trajectory. Growth curve models can accurately estimate effects of feeding practices on infant growth to direct obesity prevention efforts.

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