Journal of Applied Physiology, Vol 66, Issue 1 370-376, Copyright © 1989 by American Physiological Society
Whole-body protein metabolism in lactating and nonlactating women
K. J. Motil, C. M. Montandon, D. L. Hachey, T. W. Boutton, P. D. Klein and C. Garza
Department of Pediatrics, Baylor College of Medicine, Houston, Texas.
The adaptive responses of body protein metabolism to lactation were
characterized in women at 1, 5, and 12 mo postpartum and in nulliparous
controls during a controlled diet of measured protein and energy intakes by
nitrogen balance, a constant infusion of [13C]bicarbonate, and a primed
constant infusion of [1-13C]leucine and [alpha-15N]-lysine. Dietary energy
intakes in the lactating women were 27% greater than those in the
nulliparous controls. Despite these differences, lactating women had
significantly lower nitrogen balances compared with the nonlactating women
(-4.0 +/- 37.8 vs. +44.7 +/- 30.8 mg.kg-1.day-1). No significant
differences in amino acid flux, oxidation, or incorporation into protein
were detected during fasting conditions in the two groups of women.
However, significantly positive associations were noted between dietary
intakes and the variables of protein metabolism in the lactating women. A
more complete understanding of the mechanisms that regulate the disposition
of dietary nutrients into maternal body stores or milk production will
enhance the determination of nutrient requirements in lactating women.
