title: Adjustments in energy expenditure and substrate utilization during late pregnancy and lactation.
abstract: BACKGROUND
  Metabolic adjustments occur during pregnancy and lactation to support fetal growth and milk synthesis; however, the effect of body composition and hormonal milieu on these changes is poorly understood.
  
  
  OBJECTIVE
  We hypothesized that energy metabolism changes during pregnancy and lactation to support fetal growth and milk synthesis, and that body composition and hormonal milieu influence these alterations.
  
  
  METHODS
  We measured energy expenditure, body composition, and hormone, metabolite, and catecholamine concentrations in 76 women (40 lactating, 36 nonlactating) at 37 wk gestation and 3 and 6 mo postpartum. Total energy expenditure (TEE), basal metabolic rate (BMR), sleeping metabolic rate (SMR), and minimal SMR (MSMR) were measured with room calorimetry. Fat-free mass (FFM) and fat mass were estimated with a 4-component model.
  
  
  RESULTS
  TEE, BMR, SMR, and MSMR were 15-26% higher during pregnancy than postpartum after being adjusted for FFM, fat mass, and energy balance. TEE, SMR, and MSMR were higher in lactating than in nonlactating women. Fasting serum insulin, insulin-like growth factor I, fatty acids, and leptin, and 24-h urinary free norepinephrine, epinephrine, and dopamine correlated positively with TEE, BMR, SMR, and MSMR. In nonlactating women, the respiratory quotient decreased over time, carbohydrate oxidation decreased, and fat oxidation increased. Substrate utilization was not influenced by body composition, fasting serum hormones, or 24-h urinary catecholamines.
  
  
  CONCLUSIONS
  These results indicate increased energy expenditure and preferential use of carbohydrates during pregnancy and lactation. Elevated respiratory quotient and carbohydrate utilization during pregnancy continue during lactation, consistent with preferential use of glucose by the fetus and mammary gland.
authors.affiliation: US Department of Agriculture, Agricultural Research Service Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA. nbutte@bcm.tmc.edu
authors.forename: N F
authors.initials: NF
authors.lastname: Butte
authors.forename: J M
authors.initials: JM
authors.lastname: Hopkinson
authors.forename: N
authors.initials: N
authors.lastname: Mehta
authors.forename: J K
authors.initials: JK
authors.lastname: Moon
authors.forename: E O
authors.initials: EO
authors.lastname: Smith
mesh_terms: D000293:Adolescent; D000328:Adult; D001481:Basal Metabolism; D001823:Body Composition; D002151:Calorimetry; D002395:Catecholamines / Q000652:urine; D004734:Energy Metabolism; D005215:Fasting; D005260:Female; D006728:Hormones / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000652:urine; D007774:Lactation / Q000378:metabolism*; D049590:Postpartum Period; D011247:Pregnancy / Q000378:metabolism*; D011263:Pregnancy Trimester, Third