LAUSR

Aim The aim of this study was to examine the relationship between breastfeeding and postpartum maternal weight change. Method This study used data from the Japan Environment and Children’s Study (JECS), an ongoing nationwide birth cohort study. Participants were categorized into two groups: full breastfeeding (FB) and non-full breastfeeding (NFB) groups. Postpartum weight changes between the FB (n = 26,340) and NFB (n = 38,129) groups were compared. Results At 6 months postpartum, mean weight retention was significantly lower in the FB group than in the NFB group (0.2 vs 0.8 kg, respectively, p<0.001). Weight retention differed by pre-pregnancy body mass index (BMI), with postpartum weights of overweight (pre-pregnancy BMI 25.0–29.9) and obese (pre-pregnancy BMI ≥30.0) participants being lower than pre-pregnancy weight; this trend was more pronounced in the FB group than in the NFB group (overweight: −2.2 vs −0.7 kg, respectively; obese: −4.8 vs −3.4 kg, respectively). Factors affecting weight retention at 6 months postpartum were weight gain during pregnancy (β = 0.43; p<0.001), pre-pregnancy BMI (β = −0.147; p<0.001) and feeding method. FB resulted in lower weight retention than NFB (β = −0.107; p<0.001). Conclusion Breastfeeding reduced maternal weight retention, which was greater in mothers who were obese before pregnancy. For obese women, active breastfeeding may improve their health.