Em. Heath et al., BIOELECTRIC IMPEDANCE AND HYDROSTATIC WEIGHING WITH AND WITHOUT HEAD SUBMERSION IN PERSONS WHO ARE MORBIDLY OBESE, Journal of the American Dietetic Association, 98(8), 1998, pp. 869-875
Objective To compare hydrostatic weighing with and without head submer
sion and bioelectric impedance analysis (BIA) for measurement of body
composition of persons who are morbidly obese. Design 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. Subjects Subjects
were 16 morbidly obese men (142.5 kg mean body weight) and 30 morbidl
y obese women (125.9 kg mean body weight) living in the Salt Lake Coun
ty, Utah, area. Morbid obesity was defined as 40 kg or more over ideal
weight. Statistical analysis One-way, repeated-measures analysis of v
ariance was followed by Scheffe post hoc tests; body-fat measurement m
ethod served as the repeated variable and percentage of body fat as th
e dependent variable. Men and women were analyzed separately. In addit
ion, degree of agreement between the 3 methods of determining body com
position was determined. A regression equation was used to calculate b
ody density for hydrostatic weighing without head submersion. Two new
BIA regression equations were developed from the data of the 16 men an
d 30 women. Results Values for percentage body fat from hydrostatic we
ighing 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%, respect
ively, P<.0001). Values for body fat percentage measured by BLA were s
ignificantly lower for men (36.1%) and women (43.1%) (for both, P<.000
1) compared with values from hydrostatic weighing methods. BIA underpr
edicted percentage body fat by a mean of 5.7% in men and 9.1% in women
compared with the traditional hydrostatic weighing method. Applicatio
ns/conclusions BIA tended to underpredict the measurement of percentag
e body fat in male and female subjects who were morbidly obese. Hydros
tatic weighing without head submersion provides an accurate, acceptabl
e, and convenient alternative method for body composition assessment o
f the morbidly obese population in comparison with the traditional hyd
rostatic weighing method. In population screening or other settings wh
ere underwater weighing is impractical, population-specific BIA regres
sion equations should be used because general BIA equations lead to co
nsistent underprediction of percentage body fat; compared with hydrost
atic weighing.