Validity of segmental multiple-frequency bioelectrical impedance analysis to estimate body composition of adults across a range of body mass indexes.

OBJECTIVE We compared body composition estimates using an eight-electrode, segmental, multiple-frequency bioelectrical impedance analysis (segmental MF-BIA) and dual x-ray absorptiometry (DXA) in a group of healthy adults with a range of body mass indexes (BMIs). METHODS Percentage of body fat (%BF), fat-free mass, and fat mass assessed by DXA and segmental MF-BIA in 132 healthy adults were classified by normal (N; 18.5-24.9 kg/m(2)), overweight (OW; 25-29.9 kg/m(2)), and obese (OB; 30-39.9 kg/m(2)) BMI. RESULTS Compared with DXA, segmental MF-BIA overestimated %BF in the OB BMI group (3.4%; P < 0.0001). MF-BIA overestimated %BF among men (0.75%; P < 0.006) and women (0.87%; P < 0.006) and underestimated it in the N BMI group (-1.56%; P < 0.0001); %BF was not different between methods in the OW BMI group. Error in %BF determined by segmental MF-BIA and DXA increased as %BF increased (r = 0.42, P < 0.0001). Waist circumference was the only significant predictor of systematic error in %BF between MF-BIA and DXA (r = 0.60, P < 0.0001). CONCLUSION Eight-electrode, segmental MF-BIA is a valid method to estimate %BF in adults with BMI classified as N and OW, but not as OB. Estimation of trunk resistance with current segmental MF-BIA devices may explain the underestimation of %BF in the adults with OB BMI. Further examination of the effect of waist circumference and body fat distribution on the accuracy of BIA measurements is warranted.