Discriminating between body fat and fluid changes in the obese adult using bioimpedance vector analysis.
OBJECTIVE
Conventional body composition methods may produce biased quantification of fat and fat-free mass in obese subjects, due to possible violation of the assumption of constant (73%) tissue hydration. We used an assumption-free, graphical method for interpreting body weight variation in obesity using bioelectrical measurements.


METHODS
540 obese subjects with body mass index (BMI) > 31 kg/m2 without apparent edema were compared to 726 healthy subjects with BMI < 31 kg/m2 and to 50 renal patients with apparent edema. A subgroup of 48 obese subjects were evaluated again after weight loss (8.6 kg, 3 BMI units) following one-month energy restriction (5 MJ/d, 1200 kcal/d). 32 obese uremic patients were evaluated before and after a dialysis session (3.2 kg fluid removed). Direct measurements obtained from standard 50 kHz frequency bioelectrical impedance analyzer were used as impedance vectors in the Resistance-Reactance Graph.


RESULTS
1) Impedance vectors of obese subjects could be discriminated from those of edematous patients with 91% correct allocation; 2) A significant lengthening of vectors was observed after fluid loss of 3 kg in obese subjects; but 3) A body weight loss of about 9 kg after energy restriction was associated with no vector displacement.


CONCLUSIONS
A different impedance vector pattern was associated with body weight loss in obesity due to fluid removal (vector lengthening) versus an energy-restricted diet (no vector displacement).
Piccoli
A
A
Institute of Internal Medicine, Division of Nephrology, University of Padova, Italy. apiccoli@ux1.unipd.it
Brunani
A
A
Savia
G
G
Pillon
L
L
Favaro
E
E
Berselli
M E
ME
Cavagnini
F
F
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition; D015331:Cohort Studies; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D004038:Diet, Reducing; D004487:Edema / Q000209:etiology / Q000503:physiopathology; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000150:complications; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009765:Obesity / Q000178:diet therapy* / Q000503:physiopathology; D012016:Reference Values; D012737:Sex Factors