Measurement of body composition changes with weight loss in postmenopausal women: comparison of methods.

BACKGROUND

The accurate measurement of body composition changes is important when evaluating the efficacy of medical nutrition therapy and weight management programs, yet is not well documented in older women.

OBJECTIVE

We compared methods of estimating energy-restriction-induced body composition changes in postmenopausal women.

DESIGN

27 women (59 +/- 8 y; BMI 29.0 +/- 2.9 kg/m2; mean +/- SD) completed a 9-wk energy restriction period (5233 kJ/d, (1250 kcal/d)). Changes in % body fat (delta%BF), fat mass (deltaFM), and fatfree mass (deltaFFM) were measured by hydrostatic weighing (HW), air-displacement plethysmography (ADP), dual-energy x-ray absorptiometry (DXA), and deuterium oxide dilution (D2O). The Baumgartner et al. (Am J Clin Nutr 53:1345-1353, 1991) four-compartment (4C) model with body volume from HW was the criterion method. The 4C model with body volume from ADP was also compared. Regression equations were developed based on 4CHW (dependent variable) utilizing results of change (POST-PRE) for each method.

RESULTS

The women lost 6.8 +/- 3.2 kg; 9% of baseline weight. Based on 4CHW, the body composition changes were -2.4 +/- 4.5 delta%BF, -4.7 +/- 3.3 kg deltaFM, and -2.6 +/- 4.4 kg deltaFFM. No differences were detected by ANOVA for delta%BF, deltaFM, and deltaFFM among 4CHW, HW, ADP, DXA, D2O, and 4CADP. Bland-Altman limits of agreement showed differences between methods that ranged from 14.5 to -14.1 delta%BF, 7.8 to -8.1 kg deltaFM, and 7.5 to -8.4 kg deltaFFM for individuals. A bias was shown with 4CADP overestimating delta%BF (1.4 %) and FM (0.6 kg) and underestimating deltaFFM (-1.2 kg) compared to 4CHW. The regression model was acceptable for %BF (4CADP, 2CHW, and 2CD2O); FM and FFM (4CADP, 3CDXA, 2CHW, and 2CD2O), but not for other estimates of %BF, FM, FFM.

CONCLUSIONS

These body composition assessment methods may be used interchangeably to quantify changes in % body fat, fat mass, and fat-free mass with weight loss in groups of postmenopausal women. 4CADP overestimates delta%BF and underestimates deltaFFM. When utilizing one of these comparison methods (4CADP, 3CDXA, 2CHW, 2CD2O) to quantify changes in fat mass and fat-free mass for an individual postmenopausal woman, regression equations may be used to relate the data to 4CHW.