Response to messaging and methodological considerations when researching breastfeeding and obesity

Abstract

We thank the Manitoba Interdisciplinary Lactation Center group for their thorough analysis and comment on our research [1]. As we understand it, Reyes et al. [2] raise concerns regarding (i) the methodologic limitations of our research and (ii) the messaging around breast milk of mothers with obesity. In response to the methodologic limitations, we have fully acknowledged in our discussion the limitations raised by Reyes et al. We have proposed that our findings, along with the similar findings of Fields et al., Isganaitis et al., and Sims et al. [3–6], lay the groundwork for future prospective studies designed to investigate this association in women with overweight and obesity, taking into account important variables such as diet, activity, and detailed sociodemographic factors, or randomized controlled trials, to further limit confounding. The goal of our study was to determine the association between maternal body mass index (BMI), breast milk composition, and infant growth trajectories. We performed regression analysis to identify these associations. Ideally, mediation analysis would have also been performed to identify if a causal relationship was present. However, given our small sample size, we were underpowered for mediation analysis, which we have fully acknowledged in our limitations. Nevertheless, even in this small sample size, we did identify an association between maternal BMI and breast milk omega-6 (n-6) to omega-3 (n-3) polyunsaturated fatty acid (PUFA) ratio. We also found that a higher ratio of breast milk n-6:n-3 PUFA was associated with a higher BMI zscore trajectory in infancy. We are not the first to note the association between maternal BMI and breast milk with higher concentrations of pro-inflammatory markers [6–8]. In fact, others have also commented on the role of similar breast milk markers or components in the relationship between maternal BMI and child adiposity accrual [4–6]. We did not have information on complementary feeding in our cohort, but we observed differences in infant growth outcomes emerge before complementary feeding could plausibly begin. We believe it is imperative to present this objective data to provide a catalyst for future studies aiming to identify if a causal relationship is present. Regarding the messaging of our study, Reyes et al. [2] claim that breastfeeding has been shown to decrease childhood obesity. In fact, this is controversial and has only been reported in observational studies, which are subject to