title: Assessment of fat-free mass from bioelectrical impedance analysis in obese women with Prader-Willi syndrome.
abstract: BACKGROUND
  Fat-free mass (FFM) is lower in obese subjects with Prader-Willi syndrome (PWS) than in obese subjects without PWS. FFM prediction equations developed in non-PWS subjects may, thus, not work in PWS subjects.
  
  
  OBJECTIVE
  To test whether the estimation of FFM from bioelectrical impedance analysis (BIA) in PWS subjects requires population-specific equations.
  
  
  METHODS
  Using dual-energy X-ray absorptiometry, this study measured FFM in 27 PWS and 56 non-PWS obese women and evaluated its association with the impedance index at 50 kHz (ZI50), i.e. the ratio between squared height and whole-body impedance at 50 kHz.
  
  
  RESULTS
  At the same level of ZI50, PWS women had a lower FFM than non-PWS women. However, when PWS-specific equations were used, FFM was accurately estimated at the population level. An equation employing a dummy variable coding for PWS status was able to explain 85% of the variance of FFM with a root mean squared error of 3.3 kg in the pooled sample (n = 83).
  
  
  CONCLUSIONS
  Population-specific equations are needed to estimate FFM from BIA in obese PWS women.
authors.affiliation: a Liver Research Center , Basovizza , Trieste , Italy .|b International Center for the Assessment of Nutritional Status (ICANS), University of Milano , Milano , Italy .
authors.forename: Giorgio
authors.initials: G
authors.lastname: Bedogni
authors.affiliation: c Istituto Auxologico Italiano, IRCCS , Division of Auxology and Metabolic Diseases , Verbania , Italy , and.|d Istituto Auxologico Italiano, IRCCS , Experimental Laboratory for Auxo-Endocrinological Research , Milano and Verbania , Italy.
authors.forename: Graziano
authors.initials: G
authors.lastname: Grugni
authors.affiliation: d Istituto Auxologico Italiano, IRCCS , Experimental Laboratory for Auxo-Endocrinological Research , Milano and Verbania , Italy.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Tringali
authors.affiliation: d Istituto Auxologico Italiano, IRCCS , Experimental Laboratory for Auxo-Endocrinological Research , Milano and Verbania , Italy.
authors.forename: Fiorenza
authors.initials: F
authors.lastname: Agosti
authors.affiliation: c Istituto Auxologico Italiano, IRCCS , Division of Auxology and Metabolic Diseases , Verbania , Italy , and.|d Istituto Auxologico Italiano, IRCCS , Experimental Laboratory for Auxo-Endocrinological Research , Milano and Verbania , Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sartorio
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007558:Italy; D008875:Middle Aged; D011218:Prader-Willi Syndrome / Q000453:epidemiology* / Q000235:genetics; D055815:Young Adult
keywords: Bioelectrical impedance analysis; Prader-Willi syndrome; body composition; dual energy X-ray absorptiometry; prediction equations