Body Composition and Energy Expenditure Changes during Weight Loss: An Exploratory Study

The objective of this exploratory study was to describe changes in body composition and resting energy expenditure (REE) in adult women during weight reduction. A total of 69 client records were collected retrospectively from a 25 week commercial weight loss program that restricted calories to 90% of measured REE. Data analyzed included total body mass (TBM), fat mass (FM) and fat-free mass (FFM) from air displacement plethysmography; measured REE from indirect calorimetry; and predicted REE from linear regression. From baseline to week 25, there were significant declines in TBM (95.0 ± 24.1 kg to 87.2 ± 22.9 kg; P < 0.001) and FM (47.5 ± 18.5 kg to 39.9 ± 17.6 kg; P < 0.001). During the same time period, FFM remained unchanged (47.5 ± 7.3 kg to 47.2 ± 7.0 kg; P ≥ 0.05). REE was signifycantly lower at weeks 13 (6595.2 ± 1312.1 kJ) and 25 (6608.2 ± 1404.6 kJ) compared to baseline (7117.4 ± 1471.5 kJ) (P < 0.001); however, REE at weeks 13 and 25 were similar (P ≥ 0.05). At weeks 13 and 25, predicted REE (6992.7 ± 1065.7 and 6939.2 ± 1056.0 kJ, respectively) was significantly higher than measured REE (6595.2 ± 1312.1 and 6608.2 ± 1404.6 kJ, respectively) (P < 0.001). The results of this study suggest that significant reduction in TBM is possible without the loss of FFM and that metabolic adaptation may occur during the process.