Giorgio Bedogni1,2, Graziano Grugni3,4, Gabriella Tringali4, Fiorenza Agosti4, Alessandro Sartorio3,4. 1. a Liver Research Center , Basovizza , Trieste , Italy . 2. b International Center for the Assessment of Nutritional Status (ICANS), University of Milano , Milano , Italy . 3. c Istituto Auxologico Italiano, IRCCS , Division of Auxology and Metabolic Diseases , Verbania , Italy , and. 4. d Istituto Auxologico Italiano, IRCCS , Experimental Laboratory for Auxo-Endocrinological Research , Milano and Verbania , Italy.
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. AIM: 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). CONCLUSION: Population-specific equations are needed to estimate FFM from BIA in obese PWS women.
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. AIM: 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 obesewomen 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, PWSwomen had a lower FFM than non-PWSwomen. 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). CONCLUSION: Population-specific equations are needed to estimate FFM from BIA in obese PWSwomen.
Entities:
Keywords:
Bioelectrical impedance analysis; Prader-Willi syndrome; body composition; dual energy X-ray absorptiometry; prediction equations
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