Linking maternal BMI trajectories from prepregnancy to postpartum with breast milk fat composition: a retrospective longitudinal study

Fat, as one of the macronutrients in breast milk (BM) plays an important role in infant growth and development. This study aimed to explore the impact of maternal body mass index (BMI) trajectories in different pregnancy periods on the fat composition of BM and clarify the possible metabolic mechanisms. A retrospective longitudinal study was conducted in central south China and a total of 195 lactating women was recruited. Prepregnancy and delivery maternal weights were obtained from the Medical Birth Registry, while postpartum weight and height were measured during the interview. BM macronutrients and fatty acid (FA) profiles were analyzed. Maternal BMI trajectories reflected the combined weight status in different pregnancy periods was identified by Latent Class Growth Model. The associations of BM fat compositions with maternal weight status were used by multiple linear regression analysis. Two maternal BMI trajectories characterized by high and low maternal BMI were found from prepregnancy to postpartum. The maternal BMI trajectories was positively associated with BM fat (β = 0.233, 95%CI: 0.092, 0.374), energy (β = 0.208, 95%CI:0.065, 0.351), and saturated fatty acids (SFAs) (0.160, 95%CI: 0.014, 0.306). Moreover, these fat compositions were also positively associated with prepregnancy overweight and obesity. The subgroup analysis by lactaing period found that in both subgroups, BM fat concentration was positively associated with maternal BMI trajectory and prepregnancy overweight and obesity. In addition, the results also revealed that in the lactation period of 90–180 days, maternal prepregnancy overweight and obesity were positively associated with BM concentrations of SFA, n‑6 PUFA, and total FAs. BM fat and energy were positively correlated with BM main FAs C14:0, C16:0, and C18:1n-9, which were associated with diet intake and endogenous synthesis of SFA. High maternal BMI trajectory from prepregnancy to postpartum impacted BM fat and energy. The impact mainly depended on the maternal prepregnancy weight status. The potential metabolic mechanisms of maternal weight status on BM fat were associated with SFA endogenous synthesis.