Differences in resting metabolic rate between paraplegic and able-bodied subjects are explained by differences in body composition

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Abstract
Background: Little is known about the relation between body composition and energy metabolism in paraplegia. Objective: We investigated the relation between body composition and energy metabolism in healthy paraplegics as compared with able-bodied control subjects. We hypothesized that paraplegics would have lower fat-free mass (FFM), body cell mass (BCM), resting metabolic rate (RMR), and thermic effect of feeding (TEF). Design: This cross-sectional study included 34 control subjects and 28 paraplegics (mean age: 29.1 ± 7.6 and 33.9 ± 9.2 y, respectively) with body mass indexes (in kg/m2) of 23.5 ± 1.8 and 24.3 ± 6.0, respectively. We measured RMR and TEF with indirect calorimetry, total body water with deuterium dilution, and extracellular water with corrected bromide space. We calculated FFM (total body water/0.732) and BCM [(total body water − extracellular water)/0.732)]. Results: FFM was higher in control subjects than in paraplegics (77.2 ± 7.2% and 69.2 ± 8.7%, respectively; P = 0.0002), as were BCM (47.4 ± 6.7% and 35.9 ± 8.1%, respectively; P < 0.0001) and RMR (7016 ± 935 and 6159 ± 954 kJ/d, respectively; P = 0.0007). FFM was the single best predictor of RMR in both groups (r2 = 0.83 for control subjects and 0.70 for paraplegics, P < 0.0001 for both). RMR adjusted for FFM did not differ significantly between control subjects and paraplegics (6670 ± 504 and 6588 ± 501 kJ/d, respectively). TEF also did not differ significantly between control subjects and paraplegics (6.25 ± 2.2% and 5.53 ± 1.8% of energy intake, respectively). Conclusions: FFM, BCM, and RMR, but not obligatory TEF, are lower in paraplegics than in control subjects. RMR does not differ between control and paraplegic subjects after adjustment for FFM, indicating similar metabolic activity in the fat-free compartment of the body.