Bioelectric impedance and hydrostatic weighing with and without head submersion in persons who are morbidly obese.
OBJECTIVE
To compare hydrostatic weighing with and without head submersion and bioelectric impedance analysis (BIA) for measurement of body composition of persons who are morbidly obese.


METHODS
Body composition was determined using 3 methods: hydrostatic weighing with and without head submersion and BIA. Residual volume for the hydrostatic weighing calculation was determined by body plethysmography.


METHODS
Subjects were 16 morbidly obese men (142.5 kg mean body weight) and 30 morbidly obese women (125.9 kg mean body weight) living in the Salt Lake County, Utah, area. Morbid obesity was defined as 40 kg or more over ideal weight.


METHODS
One-way, repeated-measures analysis of variance was followed by Scheffé post hoc tests; body-fat measurement method served as the repeated variable and percentage of body fat as the dependent variable. Men and women were analyzed separately. In addition, degree of agreement between the 3 methods of determining body composition was determined. A regression equation was used to calculate body density for hydrostatic weighing without head submersion. Two new BIA regression equations were developed from the data of the 16 men and 30 women.


RESULTS
Values for percentage body fat from hydrostatic weighing with and without head submersion (41.8% vs 41.7%, respectively) were the same for men but differed for women (52.2% vs 49.4%, respectively, P < .0001). Values for body fat percentage measured by BIA were significantly lower for men (36.1%) and women (43.1%) (for both, P < .0001) compared with values from hydrostatic weighing methods. BIA underpredicted percentage body fat by a mean of 5.7% in men and 9.1% in women compared with the traditional hydrostatic weighing method.


CONCLUSIONS
BIA tended to underpredict the measurement of percentage body fat in male and female subjects who were morbidly obese. Hydrostatic weighing without head submersion provides an accurate, acceptable, and convenient alternative method for body composition assessment of the morbidly obese population in comparison with the traditional hydrostatic weighing method. In population screening or other settings where underwater weighing is impractical, population-specific BIA regression equations should be used because general BIA equations lead to consistent underprediction of percentage body fat compared with hydrostatic weighing.
College of Nursing and Health Sciences, University of Texas at El Paso 79902-0581, USA.
E M
EM
Heath
T D
TD
Adams
M M
MM
Daines
S C
SC
Hunt
D000328:Adult; D000704:Analysis of Variance; D001823:Body Composition; D001835:Body Weight; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000473:pathology*; D012727:Sex Characteristics