Maternal Physical Activity and Its Relationship to the Human Milk Metabolome and Infant Body Composition

Exercise is recommended for postpartum health, but its effects on breast milk composition and offspring are understudied.

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.

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.

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.

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.