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.
Subject(s)
Absorptiometry, Photon , Adipose Tissue/pathology , Body Composition , Body Water/metabolism , Gastric Bypass , Indicator Dilution Techniques , Obesity/surgery , Adipose Tissue/diagnostic imaging , Adipose Tissue/metabolism , Adiposity , Bone Density , Bromides , Deuterium , Female , Humans , Longitudinal Studies , Minnesota , Models, Biological , Muscle, Skeletal/pathology , Obesity/diagnostic imaging , Obesity/metabolism , Obesity/pathology , Predictive Value of Tests , Radioisotope Dilution Technique , Reproducibility of Results , Sodium Compounds , Time Factors , Treatment Outcome , Weight LossABSTRACT
BACKGROUND: The most common clinical method for resting energy expenditure (REE) assessment is prediction equations. The purpose of this study was to elucidate which prediction equation is most accurate for REE assessment in extremely obese women. METHODS: Fourteen extremely obese women (mean +/- SD body mass index: 49.8 +/- 6.2 kg/m(2); age: 49 +/- 10 years) were measured for height and weight and REE via indirect calorimetry (IC) by a metabolic cart system. Predicted REE was evaluated by several equations, including Harris-Benedict with actual body weight, Harris-Benedict with several adjustments to body weight, Cunningham, Mifflin-St Jeor, Owen, World Health Organization (WHO), and Bernstein equations. Accuracy was determined by mean difference data (IC REE - equation REE; Student's paired t-test), correlation coefficients, and agreement between methods by Bland-Altman plots. Accuracy was also evaluated on an individual basis, defined by the percentage of individuals within +/-10% of IC REE. RESULTS: The Mifflin-St Jeor, Harris-Benedict with actual body weight, and the WHO equations were the most accurate in terms of mean predicted REE. The mean predicted REE values by all other equations were different from the IC REE values (p < .1). According to the individual data, the Mifflin-St Jeor was most accurate (14% outside +/-10% IC REE). The Harris-Benedict with actual body weight and WHO equations were less accurate on individual terms, with 29% and 42% of the predicted REE values, respectively, falling outside +/-10% of IC REE. CONCLUSIONS: The Mifflin-St Jeor equation was most accurate method for REE assessment in extremely obese women.
