Hormonal and Physiological Correlates of Energy Expenditure and Substrate Oxidation in Middle-Aged, Premenopausal Women1
Michael J. Toth,
Cynthia K. Sites and
Eric T. Poehlman
Division of Clinical Pharmacology and Metabolic Research,
Department of Medicine and Division of Reproductive Endocrinology,
Department of Obstetrics and Gynecology, University of Vermont,
Burlington, Vermont 05405
Address all correspondence and requests for reprints to: Eric T. Poehlman, Ph.D., Given Building C-247, University of Vermont, Burlington, Vermont 05405. E-mail: epoehlma{at}zoo.uvm.edu
An understanding of the hormonal and physiological correlatesof energy
expenditure and substrate oxidation in middle-agedwomen will increase
our knowledge of factors that promote changesin energy balance and
adiposity. We measured resting and postprandialenergy expenditure and
substrate oxidation in 59 middle-aged,premenopausal women (mean
± SD age, 47 ± 2 yr)to examine the hormonal and
physiological correlates of energyand substrate metabolism. Energy
expenditure and substrate oxidationwere measured at rest using
indirect calorimetry and urinarynitrogen excretion and for 180 min
after the ingestion of aliquid meal (10 kcal/kg fat-free mass;
410 ± 44 Cal).Fasting hormone levels were measured by RIA,
glucose tolerancewas determined by a 75-g oral glucose tolerance test,
body compositionwas measured by dual energy x-ray absorptiometry, and
peak aerobiccapacity was determined by a treadmill test. Using
stepwiseregression analysis, we found that resting energy expenditure
waspredicted by fat-free mass and serum leptin concentration
(r2= 66%; P < 0.01), fat
oxidation was predicted by restingenergy expenditure
(r2 = 17%; P < 0.01), and
carbohydrateoxidation was predicted by serum leptin and appendicular
skeletalmuscle mass (r2 = 21%; P
< 0.01). No variables were relatedto postprandial energy expenditure
or substrate oxidation. Weconclude that in middle-aged, premenopausal
women, variationin resting energy expenditure and substrate oxidation
is primarilyexplained by fat-free mass and serum leptin levels. Thus,
changesin metabolically active tissue mass or leptin concentrationmay
partially contribute to changes in resting energy expenditureor
substrate oxidation in middle-aged women.
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