Trajectory and determinants of change in lean soft tissue over the postpartum period.

The aim of this study was to characterise changes in lean soft tissue (LST) and examine the contributions of energy intake, physical activity and breast-feeding practices to LST changes at 3 and 9 months postpartum. We examined current weight, LST (via dual-energy X-ray absorptiometry), dietary intake (3-d food diary), physical activity (Baecke questionnaire) and breast-feeding practices (3-d breast-feeding diary) in forty-nine women aged 329 (sd 38) years. Changes in LST varied from -251 to +250 kg with twenty-nine women gaining LST (11 (sd 07) kg, P<0001) and twenty women losing LST (-09 (sd 08) kg, P<0001). Energy intake (133 (SD 42) v. 109 (SD 33) kJ/kg, P=0019) and % kJ from fat at 3 months postpartum was higher in women who gained LST at 9 months postpartum (gained LST=34 (sd 5) % kJ; lost LST=29 (sd 4) % kJ, P=0002). Women who gained LST reported breast-feeding their infants more frequently (gained LST=8 (sd 3) feeds/d; lost LST=5 (sd 1) feeds/d, P=0014) and for more time per d (gained LST=115 (sd 78) min/d; lost LST=59 (sd 34) min/d, P=0016) at 9 months postpartum. Energy intake and % kJ from fat at 3 months were significant predictors of LST gain (beta=008 (se 004) and 024 (se 009), respectively). This suggests that gain in LST may be associated with more frequent and longer episodes of breast-feeding at 9 months postpartum as well as dietary intake early in the postpartum period.