LEAN BODY-MASS OF WELL-NOURISHED WOMEN IS PRESERVED DURING LACTATION

To determine whether the lean body mass of well-nourished women was mo bilized to support milk protein output during lactation, the body comp osition of 10 lactating and 10 nonlactating women was examined longitu dinally at 6-wk intervals between 6 and 24 wk postpartum and at 52 wk postpartum, and that of 10 nulliparous women was examined at equivalen t intervals, by using clinical anthropometry and whole-body potassium counting. Milk production was determined at 6-wk intervals during the period of exclusive breast-feeding (6-24 wk postpartum) by the test-we ighing procedure. Milk composition was determined by chemical analysis . Dietary intakes were determined at 6-wk intervals between 6 and 24 w k postpartum from 3-d food records with use of a nutrient database. Le an body mass was maintained in women who exclusively breast-fed their infants during the first 6 mo postpartum while consuming dietary prote in in amounts that exceeded those of their nonlactating counterparts b y 55%. The high protein intakes were sustained throughout lactation de spite a progressive reduction by 32% of milk protein output. Lean body mass was preserved throughout lactation in well-nourished women, sugg esting that the metabolic needs of milk protein production were met so lely by higher protein intakes of the lactating women.