A single bout of breast milk expression does not increase resting metabolic rate.

Introduction: Breastfeeding women have elevated resting metabolic rate (RMR); however, whether a single bout of lactation increases RMR is unknown. This study aimed to determine if a single bout of lactation acutely increased RMR.

Methods: Twenty-two lactating women (age: 31 ± 0.9 year, body mass index: 27.3 ± 1.2 kg/m ) were recruited. RMR was assessed at baseline and at 1- and 2-h following breast milk expression.

Results: RMR was unchanged in lactating women following a single bout of lactation (baseline: 1437 ± 39; 1 h: 1425 ± 37 2 h: 1440 ± 31 kcal/day) (p > .05). RMR was not correlated to daily milk produced (r = 0.05, p > .05), but was correlated to body mass (r = 0.74, p < .001), fat-free mass (kg) (r = 0.61, p < .01), and fat mass (kg) (r = 0.71, p < .01).

Conclusion: RMR in lactating women appears to be more related to body mass or composition in the postpartum period rather than lactation.