Maternal obesity does not influence human milk protein 15N natural isotope abundance.

Obesity increases protein metabolism with a potential effect on nitrogen isotope fractionation. The aim of this study was to test the influence of obesity on human milk extracted protein 15N natural isotope abundance (NIA) at one month post-partum and to compare human milk extracted protein 15N NIA and bulk infant hair 15N NIA. This cross-sectional observational study involved 16 obese mothers (body mass index (BMI) ≥ 30 kg m-2 before pregnancy) matched with 16 normal-weight mothers (18.5 kg m-2 ≤ BMI < 25 kg m-2) for age and pregnancy characteristics. Human milk extracted protein and bulk infant hair 15N NIA were determined by isotope ratio monitoring by mass spectrometry interfaced to an elemental analyser (IRM-EA/MS). No significant difference was found in human milk protein 15N NIA values between obese and normal-weight mothers (8.93 ± 0.48 ‰ vs. 8.95 ± 0.27 ‰). However, human milk protein 15N NIA was significantly lower than bulk infant hair 15N NIA: 8.94 ± 0.38 ‰ vs. 9.66 ± 0.69 ‰, respectively. On the basis of these results, it is concluded that human milk protein 15N NIA measured at one month post-partum is not influenced by maternal obesity. These findings suggest that 15N NIA may be exploited to study metabolism without considering maternal obesity as a confounder.