Abstract
CONTEXT: Exercise is recommended for postpartum health, but its effects on breast milk composition and offspring are understudied. OBJECTIVE: This work aimed to test whether the breast milk metabolome is altered with (i) acute exercise and/or (ii) habitual physical activity, and (iii) whether exercise-altered metabolites are associated with infant adiposity. METHODS: Milk metabolites were assessed before and after acute exercise and in association with habitual activity score in 2 independent cohorts at 2 academic medical centers. The acute exercise cohort had 15 mother-infant dyads. The habitual activity nested case-control analysis had 84 physically active "cases" and 35 inactive "controls," and was conducted in a subset of the Mothers and Infants Linked for Healthy Growth (MILk)/4M study (N = 348). The acute exercise exposure was a 30-minute moderate-intensity treadmill session. The habitual activity exposure was based on Physical Activity Recall questionnaire scores. Main outcome measures included milk metabolite relative abundance at 1-month post partum by liquid chromatography-gas chromatography mass spectrometry, and infant anthropometric and body composition measures at 1, 3, and 6 months. RESULTS: An acute exercise bout altered milk concentrations in 28 of 511 detectable metabolites (false discovery rate [FDR] < .05). In the habitual activity analysis, 4 of 454 detectable metabolites differed between active cases vs inactive controls (FDR < .05). Ten metabolites were altered (P < .05) by both exercise exposures. Of these, 4 were positively associated with fat mass index at 1 month, and 2 were associated with greater increase in body mass index z score between 1 and 3 months. CONCLUSION: Maternal exercise was associated with differences in the breast milk metabolome. Metabolites that were associated both with acute exercise and habitual activity correlated with infant adiposity measures.