title: Three-compartment model: critical evaluation based on neutron activation analysis.
abstract: There is renewed interest in Siri's classic three-compartment (3C) body composition model, requiring body volume (BV) and total body water (TBW) estimates, because dual-energy X-ray absorptiometry (DEXA) and in vivo neutron activation (IVNA) systems cannot accommodate subjects with severe obesity. However, the 3C model assumption of a constant ratio (alpha) of mineral (M) to total body protein (TBPro) and related residual mass density (D(RES)) based on cadaver analyses might not be valid across groups differing in sex, race, age, and weight. The aim of this study was to derive new 3C model coefficients in vivo and to compare these estimates to those derived by Siri. Healthy adults (n = 323) were evaluated with IVNA and DEXA and the measured components used to derive alpha and D(RES). For all subjects combined, values of alpha and D(RES) (means +/- SD, 0.351 +/- 0.043; 1.565 +/- 0.023 kg/l) were similar to Siri's proposed values of 0.35 and 1.565 kg/l, respectively. However, alpha and D(RES) varied significantly as a function of sex, race, weight, and age. Expected errors in percent body fat arising by application of Siri's model were illustrated in a second group of 264 adults, including some whose size exceeded DEXA limits but whose BV and TBW had been measured by hydrodensitometry and (2)H(2)O dilution, respectively. Extrapolation of predictions by newly developed models to very high weights allows percent fat error estimation when Siri's model is applied in morbidly obese subjects. The present study results provide a critical evaluation of potential errors in the classic 3C model and present new formulas for use in selected populations.
authors.affiliation: Exercise and Health Laboratory, Faculty of Human Movement, Technical University of Lisbon, 1495-688 Lisbon, Portugal.
authors.forename: Analiza M
authors.initials: AM
authors.lastname: Silva
authors.forename: Wei
authors.initials: W
authors.lastname: Shen
authors.forename: ZiMian
authors.initials: Z
authors.lastname: Wang
authors.forename: John F
authors.initials: JF
authors.lastname: Aloia
authors.forename: Miriam E
authors.initials: ME
authors.lastname: Nelson
authors.forename: Steven B
authors.initials: SB
authors.lastname: Heymsfield
authors.forename: Luis B
authors.initials: LB
authors.lastname: Sardinha
authors.forename: Stanley
authors.initials: S
authors.lastname: Heshka
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D001741:Black or African American; D001823:Body Composition; D001825:Body Fluid Compartments; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008903:Minerals / Q000032:analysis; D008954:Models, Biological; D009501:Neutron Activation Analysis / Q000379:methods*; D011506:Proteins / Q000032:analysis; D012016:Reference Values; D012737:Sex Factors; D044465:White People
chemical_list: D008903:Minerals; D011506:Proteins