title: Comparison of DXA and water measurements of body fat following gastric bypass surgery and a physiological model of body water, fat, and muscle composition.
abstract: Measurement of body composition changes following bariatric surgery is complicated because of the difficulty of measuring body fat in highly obese individuals that have increased photon absorption and are too large for the standard dual-energy X-ray absorptiometry (DXA) table. We reproducibly measured body composition from half-body DXA scans and compared the values of total body fat estimated from total body water (TBW) and DXA measurements before and after Roux-en-Y gastric bypass surgery (RYGB). DXA, TBW (deuterium dilution), extracellular water (ECW; bromide dilution), and intracellular water (ICW) measurement (by subtraction) were made before surgery and at 2 wk, 6 wk, 6 mo, and 12 mo after surgery. Twenty individuals completed baseline and at least four follow-up visits. DXA appeared to underestimate the fat and bone mass in extreme obesity (before surgery), whereas at 6 and 12 mo after surgery, the DXA and TBW fat measurements were similar. The ECW-to-ICW ratio was increased in obese individuals and increased slightly more after surgery. We describe a new model that explains this abnormal water composition in terms of the normal physiological changes that occur in body composition in obesity and weight loss. This model is also used to predict the muscle mass loss following RYGB.
authors.affiliation: Department of Integrative Biology and Physiology, University of Minnesota Twin Cities, 225 Food Science & Nutrition, 1334 Eckles Ave., St. Paul, MN 55108-6099, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Levitt
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Beckman
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Mager
authors.forename: Bret
authors.initials: B
authors.lastname: Valentine
authors.forename: Shalamar D
authors.initials: SD
authors.lastname: Sibley
authors.forename: Tiffany R
authors.initials: TR
authors.lastname: Beckman
authors.forename: Todd A
authors.initials: TA
authors.lastname: Kellogg
authors.forename: Sayeed
authors.initials: S
authors.lastname: Ikramuddin
authors.forename: Carrie P
authors.initials: CP
authors.lastname: Earthman
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology*; D050154:Adiposity; D001823:Body Composition; D001834:Body Water / Q000378:metabolism*; D015519:Bone Density; D001965:Bromides; D003903:Deuterium; D005260:Female; D015390:Gastric Bypass; D006801:Humans; D007201:Indicator Dilution Techniques; D008137:Longitudinal Studies; D008910:Minnesota; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000473:pathology; D009765:Obesity / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology / Q000601:surgery*; D011237:Predictive Value of Tests; D011865:Radioisotope Dilution Technique; D015203:Reproducibility of Results; D017670:Sodium Compounds; D013997:Time Factors; D016896:Treatment Outcome; D015431:Weight Loss
chemical_list: D001965:Bromides; D017670:Sodium Compounds; D003903:Deuterium; C027938:sodium bromide