Submitted to: International Journal of Obesity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/27/1997
Publication Date: N/A
Citation: Interpretive Summary: When scientists conduct studies of obesity and energy requirements, it is important to account for the subjects' changes in body composition (as in fat mass), and to have accurate measurements of the changes. Even though differences have been illustrated between body composition methods, it's often assumed that body composition changes can be accurately measured by different methods. We wanted to measure changes in fat mass in women durin the first year after childbirth, and find out the extent of agreement of different models of body composition, which are based on a number of different methods. We also wanted to know if pregnancy or lactation affected the composition of fat-free mass. Despite differences between body composition models, changes in fat-free mass and fat mass in postpartum women did not differ significantly, and we found no effect of pregnancy or lactation on the density, hydration or potassium content of fat-free mass. Therefore, standard 2-component models are acceptable for use beyond the period immediately after childbirth.
Technical Abstract: Objectives: 1) To compare 2-, 3- and 4-component models of body composition based on total body water (TBW), underwater weighing (UWW), skinfold thicknesses (SF), total body potassium (TBK), dual-energy x-ray absorptiometry (DXA), and total body electrical conductivity (TOBEC); 2) to compare postpartum changes in body composition estimated by the 2-, 3- and 4-component models; 3) to test for an effect of pregnancy or lactation on the hydration, density and potassium content of fat free mass (FFM) in postpartum women. Design: Longitudinal measurements of body composition at 3, 6 and 12 mo postpartum. Subjects: Thirty-five healthy postpartum women, aged 30.2 +/- 3.5 y. Measurements: Body composition was estimated by 2- component models based on TBW, UWW, SF, TBK, DXA, and TOBEC; 3-component models based on TBW and UWW (Fuller 3, Siri 3); and a 4-component model (Fuller 4) based on TBW, UWW and bone mineral content. Results: Despite systematic differences in the estimation of FFM and FM among models, estimated changes in FFM, FM and percent FM were not significantly different among methods, except for the 3- to 6-mo FFM and FM changes estimated from TBW, which differed from SF, DXA, TOBEC, UWW and/or TBK. By 3 mo postpartum the hydration, density and potassium content of FFM (0.73 +/- 0.02, 1.099 +/- 0.015 kg/l and 2.31 +/- 0.10 g/kg, respectively) had returned to within the normal range. Conclusion: In spite of systematic differences among body composition models for the measurement of FFM and FM, changes in FFM and FM did not differ significantly among the models. Since there was no apparent effect of pregnancy or lactation on the composition of FFM, 2-component models of body composition are acceptable for use in postpartum women beyond the puerperium.