Altered body composition affects resting energy expenditure and interpretation of body mass index in children with spinal cord injury.

BACKGROUND: Individuals with spinal cord injury (SCI) typically undergo changes in their body composition (reduction in lean body mass and an increase in fat mass) that can lead to secondary complications associated with diminished physical activity and obesity. METHODS: This study used dual energy X-ray absorptiometry (DXA) to estimate the total lean tissue mass (LTM), total body fat, and total bone mineral content (BMC) to assess the relationship between body mass index (BMI), body composition, and resting metabolic rate (RMR) in a group of children with SCI who were matched with able-bodied controls for age and sex. Body composition and RMR were measured in 18 boys and 9 girls (10-21 years of age) who had a SCI in the previous 1 to 3 years and in 27 age- and sex-matched controls. RESULTS: Children with SCI had significantly lower mean LTM than control subjects (37.6 +/- 9.6 kg and 46.7 +/- 9.2 kg, respectively; P < 0.001) and higher percent body fat (26.4 +/- 7.9% and 20.2 +/- 8.5%, respectively; P < 0.02) as measured by DXA, despite their reduced BMI (18.9 +/- 3.8 kg/m2 and 21.2 +/- 2.9 kg/m2, respectively; P < 0.01). Children with SCI had lower RMR than the controls subjects (1213 +/- 334 kJ/d and 1511 +/- 257 kJ/d, respectively), but there was no difference in RMR when adjusted for LTM. CONCLUSION: Children with SCI have lower RMRs that are associated with their reduced LTM. The reduction in LTM and RMR may predispose children with SCI to relative gains in body fat. BMI significantly underestimates body fat in children with SCI.