Background: Previous studies investigating the hypothesis that a low restin
g metabolic rate (RMR) is a cause of obesity yielded discrepant findings. T
wo explanations for these findings are the use of imprecise methods to dete
rmine obesity and a failure to control for differences in fat mass (FM) and
fat-free mass (FFM) when comparing RMR values.
Objective: This study tested the hypothesis that RMR is lower in obese than
in nonobese boys (with the use of precise methods to quantify body fatness
and with adjustment for differences in both FM and FFM).
Design: Forty Chinese Singaporean boys aged 12.8-15. 1 y were recruited. Bo
ys were classified as obese (n=20) or nonobese (n=20) on the basis of their
adiposity index (ratio of FM to FFM: >0.60 = obese, <0.40 = nonobese) dete
rmined by dual-energy X-ray absorptiometry. RMR was determined by using ind
irect calorimetry. RMR values were compared by using both linear (analysis
of covariance) and log-linear (analysis of covariance with log-transformed
data) regression to control for differences in FM and FFM.
Results: Age, height, and FFM did not differ significantly between groups.
Body mass was 13 kg greater and FM was 16 kg greater in the obese boys than
in the nonobese boys (P<0.001). After control for FFM and FM, RMR did not
differ significantly between the groups.
Conclusion: When body composition is appropriately controlled for, RMR does
not differ significantly between obese and nonobese boys.