Breastfeeding practices and weight retention at one year postpartum: The importance of breastfeeding intensity and duration

Background: Breastfeeding has been associated with lower maternal postpartum weight retention, which may reduce maternal obesity risk, but findings are equivocal, and few studies include measures of both breastfeeding duration and intensity. We assessed whether breastfeeding duration was associated with weight retention at one year postpartum, and whether breastfeeding intensity modified the association. Methods: We used Infant Feeding Practices Study-II data on 1,328 U.S. mother-infant pairs followed one year postpartum. Mothers completed near-monthly questionnaires assessing past-week frequency of infants' breast milk, formula, and food intake. Using linear regression, we examined the association between breastfeeding duration and PWR among breastfeeding mothers of term infants, controlling for maternal education, race/ethnicity, prepregnancy body mass index, marital status, and age. We tested for effect modification by breastfeeding intensity (average percentage of infant milk feedings comprising breast milk during months mothers gave any breast milk, categorized as low [≤75%], medium [76-99%], and high [100%]). Results: Mean breastfeeding duration was 9 months (SD=3.9); mean PWR at one year was 3.5 pounds (SD=14.8). PWR decreased 0.41 pounds (SE=0.12, p<.0006) for each month of breastfeeding. Breastfeeding intensity modified this effect; breastfeeding duration and PWR were associated only among women with high (100%) breastfeeding intensity, for whom each additional month of breastfeeding was associated with a 0.67-pound decrease in PWR (SE=0.27, p=0.01). Conclusions: Breastfeeding duration and reduced PWR were associated only among mothers whose infants' milk feedings were 100% breast milk. Improving breastfeeding practices may also help reduce maternal obesity risk, both of which are national health objectives.