Is the association of breastfeeding with child obesity explained by infant weight change?

Objective. Breastfeeding and infant weight change are both associated with adiposity. We examined the extent to which infant weight change mediates the association between breastfeeding and adiposity at age 3 years. Methods. We studied 884 children in a prospective cohort study. We determined breastfeeding status in the first 6 months. Our primary outcomes at 3 years were body mass index (BMI) z score and the sum of subscapular and triceps skinfold thicknesses (SS + TR); we also assessed obesity. We defined infant weight change as change in weight-for-age z score between birth and 6 months. We performed multivariable regression analyses. Results. At age 6 months, 25.0% of infants were fully breastfed. At age 3 years, mean (standard deviation) BMI z score was 0.45 (1.03). In linear regression analyses adjusted for mother's educational level, race/ethnicity, smoking, BMI, pregnancy weight gain and birth weight (adjusted for gestational age), the BMI z score of fully breastfed children was 0.17 (95% CI: -0.43, 0.09) units lower than never breastfed children. After additional adjustment for infant weight change, the estimate was attenuated (-0.03, 95% CI: -0.27, 0.20). Adjustment for infant weight change only modestly attenuated estimates for SS + TR (from -1.48 mm [95% CI: -2.52, -0.44] to -1.16 mm [95% CI: -2.18, -0.14]), and for the odds of being obese (from 0.21 [95% CI: 0.07, 0.68] to 0.29 [95% CI: 0.08, 1.05]). Conclusion. Infant weight change between birth and 6 months mediates associations of breastfeeding with BMI, but only partially with indicators of child adiposity.