Bioimpedance for severe obesity: comparing research methods for total body water and resting energy expenditure

As the acceptance of surgical procedures for weight loss in morbid obesity is increasing, clinically useful baseline and follow-up measures of total body water (TBW) and resting energy expenditure (REE) are important. Research methods such as deuterium (D(2)O) dilution and metabolic carts are problematic in the clinical setting. We compared bioimpedance analysis (BIA) predicted (Tanita TBF-310) and measured TBW and REE.

Forty-two paired presurgery studies were completed using BIA and D(2)O in patients with BMI (mean +/- s.d.) 50.2 +/- 8.8 kg/m(2) for TBW, and 30 patients with BMI 51.0 +/- 13 kg/m(2) completed paired determinations of REE with metabolic carts and the Tanita balance with weight, height, sex, and age modifiers. Regression analysis and Bland-Altman plots were applied.

When regression analysis was completed for TBW, regression line was consistent with the identity line "y = x." The intercept was not different from 0 (95% confidence interval -2.5 +/- 7.0). The slope of the line was not different from 1.0 +/- 0.1. The measured TBW 51.2 +/- 10.1 l had a correlation with the predicted 49.5 +/- 11.27 l of 0.92. There also was no significant difference (P = 0.33) between predicted (2,316 +/- 559 kcal/day) and measured REE (2,383 +/- 576 kcal/day);delta 66.7 +/- 273 kcal/day. The two measures were highly correlated (r = 0.88) with no bias detected.

These observations support the use of the BIA system calibration in subjects with severe obesity. Without the use of complex, costly equipment and invasive procedures, BIA measurements can easily be obtained in clinical practice to monitor patient responses to treatment.