title: Leg to leg bioelectrical impedance analysis of percentage fat mass in obese patients-Can it tell us more than we already know?
abstract: BACKGROUND
  Bioelectrical impedance analysis (BIA) is well tolerated, inexpensive, and readily available, but can it be used to detect with clinical precision aberrant changes in the proportion of fat mass to fat-free mass during weight loss?
  
  
  OBJECTIVE
  To assess the variance in percentage body fat mass explained by the readily available inputs and assess residual variance provided by leg-to-leg BIA scales.
  
  
  METHODS
  Using cross-sectional data from a cohort of 665 patients of Indian ethnicity presenting for bariatric surgery, we examine the determinants of percentage body fat as provided by leg-to-leg output from Tanita SC-330 BIA scales.
  
  
  RESULTS
  Four input factors-sex, weight, height, and age-contributed to provide 92% and 95% explanation in output variance for percentage fat mass (%FM) and actual fat mass, respectively, in 665 patients. Body mass index alone explained 89% and 81% of variance in %FM output for women and men, respectively. Neither weight distribution, as indicated by waist and hip circumference or waist to hip ratio, nor plasma lipids or markers of glucose metabolism contributed additional variance in %FM when controlled for the 4 key inputs.
  
  
  CONCLUSIONS
  Simple, known input variables dominate the leg-to-leg BIA output of %FM, and this may compromise the detection of aberrant changes in %FM and fat-free mass with substantial weight loss. For clinical research, validated methods not largely dependent on known inputs should be used for evaluating changes in body composition after substantial weight loss.
authors.affiliation: Clinical Obesity Research, Baker IDI Heart and Diabetes Institute, Melbourne, Australia. Electronic address: John.Dixon@bakeridi.edu.au.
authors.forename: John B
authors.initials: JB
authors.lastname: Dixon
authors.affiliation: Centre for Obesity and Digestive Surgery, Gamdevi, Mumbai, India; Institute of Minimally Invasive Surgical Sciences and Research Centre, Saifee Hospital, Mumbai, India.
authors.forename: Aparna G
authors.initials: AG
authors.lastname: Bhasker
authors.affiliation: Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Australia.
authors.forename: Gavin W
authors.initials: GW
authors.lastname: Lambert
authors.affiliation: Centre for Obesity and Digestive Surgery, Gamdevi, Mumbai, India; Institute of Minimally Invasive Surgical Sciences and Research Centre, Saifee Hospital, Mumbai, India.
authors.forename: Muffazal
authors.initials: M
authors.lastname: Lakdawala
mesh_terms: D000273:Adipose Tissue / Q000473:pathology*; D000328:Adult; D000367:Age Factors; D000368:Aged; D050110:Bariatric Surgery / Q000379:methods; D001823:Body Composition / Q000502:physiology; D050218:Body Fat Distribution; D002908:Chronic Disease; D003430:Cross-Sectional Studies; D017097:Electric Impedance; D004734:Energy Metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D007866:Leg; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009767:Obesity, Morbid / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology / Q000601:surgery; D012727:Sex Characteristics; D015431:Weight Loss / Q000502:physiology; D055815:Young Adult
keywords: Bariatric; Bariatric-metabolic surgery; Bioelectrical impedance analysis (BIA); Body fat; Chronic disease; Co-morbidity; Dual-energy x-ray absorptiometry (DXA); Fat loss; Fat-free mass; Foot-to-foot BIA.; Function; Health; Metabolic; Mortality; Obese; Obesity; Quality of life; Resting energy expenditure; Sarcopenia; Severe obesity; Strength; Surgery; Weight loss; Weight regain