Effects of breastfeeding on postpartum weight change in Japanese women: The Japan Environment and Children’s Study (JECS)

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.