title: Low resting metabolic rate in exercise-associated amenorrhea is not due to a reduced proportion of highly active metabolic tissue compartments.
abstract: Exercising women with menstrual disturbances frequently display a low resting metabolic rate (RMR) when RMR is expressed relative to body size or lean mass. However, normalizing RMR for body size or lean mass does not account for potential differences in the size of tissue compartments with varying metabolic activities. To explore whether the apparent RMR suppression in women with exercise-associated amenorrhea is a consequence of a lower proportion of highly active metabolic tissue compartments or the result of metabolic adaptations related to energy conservation at the tissue level, RMR and metabolic tissue compartments were compared among exercising women with amenorrhea (AMEN; n = 42) and exercising women with eumenorrheic, ovulatory menstrual cycles (OV; n = 37). RMR was measured using indirect calorimetry and predicted from the size of metabolic tissue compartments as measured by dual-energy X-ray absorptiometry (DEXA). Measured RMR was lower than DEXA-predicted RMR in AMEN (1,215 ± 31 vs. 1,327 ± 18 kcal/day, P < 0.001) but not in OV (1,284 ± 24 vs. 1,252 ± 17, P = 0.16), resulting in a lower ratio of measured to DEXA-predicted RMR in AMEN (91 ± 2%) vs. OV (103 ± 2%, P < 0.001). AMEN displayed proportionally more residual mass (P < 0.001) and less adipose tissue (P = 0.003) compared with OV. A lower ratio of measured to DXA-predicted RMR was associated with lower serum total triiodothyronine (ρ = 0.38, P < 0.001) and leptin (ρ = 0.32, P = 0.004). Our findings suggest that RMR suppression in this population is not the result of a reduced size of highly active metabolic tissue compartments but is due to metabolic and endocrine adaptations at the tissue level that are indicative of energy conservation.
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Karsten
authors.identifier: 0000-0002-9618-2069
authors.initials: K
authors.lastname: Koehler
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Nancy I
authors.initials: NI
authors.lastname: Williams
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Mallinson
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Emily A
authors.initials: EA
authors.lastname: Southmayd
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Heather C M
authors.initials: HC
authors.lastname: Allaway
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania mjd34@psu.edu.
authors.forename: Mary Jane
authors.initials: MJ
authors.lastname: De Souza
mesh_terms: D015502:Absorptiometry, Photon; D000222:Adaptation, Physiological; D000273:Adipose Tissue / Q000378:metabolism*; D000328:Adult; D000568:Amenorrhea / Q000209:etiology / Q000378:metabolism*; D001481:Basal Metabolism; D001823:Body Composition; D001842:Bone and Bones / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D002153:Calorimetry, Indirect; D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D004734:Energy Metabolism; D015444:Exercise; D005260:Female; D006801:Humans; D020738:Leptin / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism; D055815:Young Adult
chemical_list: D020738:Leptin; D014284:Triiodothyronine
keywords: dual-energy X-ray absorptiometry; energy deficiency; exercise-associated menstrual disturbances; lean body mass; metabolic adaptation