EFFECT OF LACTATION ON RESTING METABOLIC-RATE AND ON DIET-INDUCED AND WORK-INDUCED THERMOGENESIS

Energy metabolism was measured in 24 women before pregnancy and during lactation (2 mo postpartum). Resting metabolic rate (RMR) increased by 0.17+/-0.38 kJ/min and postprandial metabolic rate (PPMR) showed a similar increase (0.17+/-0.45 kJ/min). Thus, the thermic effect of the meal (PPMR minus RMR) was not affected by lactation. Between subjects, the lactation-induced increase in RMR appeared to be positively related to body weight. During lactation gross metabolic rates during cycling (CMR) were slightly reduced and net metabolic rates during cycling (CMR minus RMR) tended to decrease by 0.6 kJ/min at all workloads; however, the decrease was statistically significant only at the lowest workload. Changes in metabolic rate during the recovery period after exercise were not significant, but resembled changes in RMR rather than changes in CMR. We conclude that no major changes in metabolic efficiency occurred during lactation.