Body composition changes in the first year postpartum among breastfeeding women living in Palmerston North, New Zealand : Mother and Infant Nutrition Investigation (MINI) study : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Auckland, New Zealand

Abstract

Background: Postpartum weight retention (PPWR) is the retention of weight gained during pregnancy, carried into the postpartum period. The consequences of PPWR for both subsequent pregnancies and long-term health have been studied in detail and can include overweight and obesity and their associated comorbidities. PPWR is affected by several factors, however, the influence of infant feeding mode is subject to conflicting results. Postpartum women in New Zealand have not been studied for their postpartum weight change patterns or the influence of infant feeding status. Aim: To explore maternal body composition changes at 3-, 6-, and 12-months postpartum in conjunction with infant feeding mode, and to validate bioelectrical impedance analysis (BIA) in assessing body composition in this population. Method: This was a secondary analysis based on the data collected from the Mother and Infant Nutrition Investigation Study, an observational longitudinal cohort study, from Palmerston North, New Zealand. Breastfeeding women had body composition assessment measures taken at 3-, 6-, and 12-months postpartum (MPP). Total body weight (TW), fat mass (FM), fat free mass (FFM), and body fat percentage (BF%) measures were collected via BIA and BOD POD (air displacement plethysmography). Participants’ demographic information and infant feeding mode were collected via a maternal questionnaire. Infant feeding mode at 3MPP (EBF - exclusive breastfeeding or MF - mixed feeding) was used to assess its impact on body composition changes. Statistical analyses were performed using IBM SPSS Statistics, carrying out descriptive statistics, repeated measures ANOVA, Pearson’s rank correlation, and cross-classification agreement. Results: 87 participants with mean (± Standard Deviation (SD)) age 31.5 ± 4.2 years, were recruited. The mean prepregnancy BMI tended to be higher for the MF group (26.2kg/m2), compared to the EBF group (23.8kg/m2), though the difference was not significant. Mean (geometric, 95% CI) prepregnancy weight was significantly lower at 66.8 (64.0, 69.8) kg than the mean (geometric, 95% CI) total weight at 12MPP (68.9 (65.3, 72.8) kg) (p = 0.046), resulting in a mean (geometric, 95% CI) weight retention of 3.14 (2.1, 4.7) kg. All participants showed significant changes at 3MPP, 6MPP, and 12MPP for all measures of body composition. TW, FM, and BF% showed a significant reduction over time points (p < 0.001), while FFM showed a significant increase at 6MPP (p < 0.001). At 3MPP 83% of participants were EBF. There were significant differences between infant feeding groups for FM, TW, BF%, but not for FFM. However, when combining time and infant feeding mode, there was no statistical significance. Body composition measurements via BIA and BOD POD were strongly associated (p < 0.001), and were classified into the same tertiles, with k-statistic agreement levels between 0.5 (moderate) to > 0.80 (very good). Conclusion: Total body weight, fat mass, and body fat percentage reduced in the postpartum period, irrespective of infant feeding mode at 3MPP. No significant difference was observed between infant feeding groups. However, on average, women had gained weight at 12MPP when compared to prepregnancy weight. Additionally, BIA showed high correlations across all measures of body composition when compared to BODPOD, further supporting the use of BIA in the postpartum population.