ARS | Publication request: ADJUSTMENTS IN ENERGY EXPENDITURE AND SUBSTRATE UTILIZATION DURING LATE PREGNANCY AND LACTATION

Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 18, 1998
Publication Date: N/A

Interpretive Summary: Many changes occur in a woman's body during pregnancy and lactation. We theorized that energy metabolism changes during pregnancy and lactation in response to the demands of the fetus and the synthesis of milk, respectively, and that it is affected by the mother's body composition and hormone status. We measured hormone levels and body composition in 76 women, about half of whom were lactating, at 37 weeks gestation and 3 and months after giving birth. We found higher rates of energy expenditure and preferred use of carbohydrate during pregnancy and lactation. Certain hormones, including epinephrine and dopamine, were positively associated with total energy expenditure and metabolic rate measurements. The higher respiratory quotient and net carbohydrate oxidation during pregnancy continued during lactation, which may pertain to the marked use of glucose of the fetus and mammary gland. As we expected, energy expenditure was influenced by body composition and hormone status. This is useful scientific data in terms of understanding and contributing to the health and physical needs of mothers and children.

Technical Abstract: Background: Numerous metabolic adjustments occur during pregnancy and lactation in order to support fetal growth and milk synthesis. We hypothesized that energy metabolism is altered during pregnancy and lactation, and that it is influenced by maternal body composition and hormonal status. Calorimetry, body composition and hormones/metabolites were measured in 76 women (40 lactating) at 37 wk gestation, and at 3 and mo postpartum. Total energy expenditure (TEE), basal metabolic rate (BMR), sleeping metabolic rate (SMR) and minimal sleeping metabolic rate (MSMR) were measured in room calorimeters for 24 h. Fat-free mass (FFM) and fat mass (FM) were estimated from weight, total body water, body volume, and bone mineral content. Adjusted for FFM and FM, TEE, BMR, SMR, and MSMR were 15-26% higher during pregnancy than postpartum. TEE, SMR and MSMR were significantly higher in lactating than nonlactating women. Serum insulin, IGF-1, free fatty acids, leptin, 24-h urinary free norepinephrine, epinephrine and dopamine were positively associated with TEE, BMR, SMR, and MSMR. Respiratory quotient (RQ) decreased among nonlactating, but not lactating women. Carbohydrate oxidation (%TEE) decreased, and fat oxidation (%TEE) increased in nonlactating women. Oxidation rates (%TEE) were not influenced by body composition or hormonal status. These results indicate increased rates of energy expenditure and preferential use of carbohydrates during pregnancy and lactation. The elevated RQ and net carbohydrate oxidation during pregnancy continue during lactation, consistent with preferential use of glucose by the fetus and mammary gland. We conclude that energy expenditure, but not substrate oxidation, is influenced by body composition and hormonal status during pregnancy and lactation.