RESTING METABOLIC RATE (RMR) IN OBESE AND NON-OBESE SINGAPOREAN BOYS AGED 13 TO 15 YEARS.

Abstract

1500 It has recently been shown that mathematical ratios may lead to spurious results when making group comparisons of RMR and analysis of covariance(ANCOVA) has been recommended instead (Poehlman and Toth, AJCN 61: 482-5, 1995). The present study compared RMR in 20 obese and 20 non-obese Singaporean boys using both the ratio method and ANCOVA to adjust for differences in fat free mass (FFM). Boys were classified via dual energy X-ray absorptiometry measurements of adiposity (fat mass/FFM) as follows: obese >0.60, non-obese<0.40. RMR was assessed using indirect calorimetry following an overnight fast. Mann-Whitney U tests showed no differences (p<0.05) between groups(obese vs non-obese, mean ± SD) for age (13.6 ± 0.5 vs 13.7± 0.6 years), height (1.64 ± 0.09 vs 1.64 ± 0.06 m) and FFM (40.5 ± 6.9 vs 44.2 ± 7.6 kg) but obese boys were heavier(74.8 ± 12.3 vs 61.8 ± 10.9 kg) and fatter (43 ± 4 vs 24± 4%) than non-obese boys (both p<0.001). RMR values are shown below(mean ± SD). TableTableIn conflict with previous work (e.g. Bandini et al. Pediatr. Res. 27: 198-203, 1990) absolute RMR did not differ between obese and non-obese boys while RMR expressed via the ratio method was higher in the obese boys. This conflict is probably attributable to the similarity in FFM between groups in the present study which is unusual because obese subjects usually have a greater FFM than non-obese subjects. Comparison of adjusted RMR values confirmed that obese boys do have a higher RMR than non-obese boys thus reaffirming the necessity of using ANCOVA when comparing RMR between groups.