The relationship between total body potassium and resting energy expenditure in individuals with paraplegia

Body composition changes occur with spinal cord injury (SCI): fat-free mass (FFM) decreases and fat mass (FM) increases. FFM has been reported to correlate with resting energy expenditure (REE) in non-SCI individuals. This report addresses the question as to whether REE correlates with measures of FFM in individuals with paraplegia. Twelve males with chronic paraplegia had measurements of total body potassium (TBK), an indicator of lean tissue, by whole body ⁴⁰K counting, and FFM by dual photon x-ray absorptiometry (FFM_dpx). REE was measured using a metabolic cart for exhaled gas analysis. Correlations between REE and TBK, and REE and FFM_dpx were determined. The mean TBK for the group was 2,850 ± 190mEq. In all subjects, TBK was below that of expected (predicted from age, height, and weight). For the group this was 34 ± 0.04% below predicted. The mean FFM_dpx was 58.3 ± 3.3kg. Following an overnight fast, REE was measured for each subject while in a seated position. The mean REE was 1,855 ± 70kcal/day. REE correlates well with both TBK (r = 0.86, p < 0.0005) and FFM_dpx (r = 0.80, p < 0.005). In summary, despite losses in metabolically active tissue in individuals with chronic paraplegia, TBK and FFM_dpx continue to have a strong relationship with REE. REE (kcal/d) may be used as an indicator of TBK or FFM_dpx using the following linear regression equations: TBK (mEq) = 2.28 · REE (kcal/d) - 1,377 (SEE = ±347) or FFM_dpx (kg) = 0.038 · REE (kcal/d) - 11.5 (SEE = ±7). In conclusion, a reduction in FFM is associated with a reduction in REE in chronic paraplegia.