Meta-analysis of resting metabolic rate in formerly obese subjects

Background: A low resting metabolic rate (RMR) for a given body size and, c omposition is partly genetically determined and has been suggested to be a risk factor for weight gain. Moreover, a low relative RMR has been reported in some, but not all, studies of formerly obese persons. The inconsistent reports may be due to a lack of statistical power to detect small differenc es in RMR and improper adjustment for body size and composition. Objective: We conducted a meta-analysis based on published studies of RMR i n formerly obese persons [body mass index (in kg/m(2)) less than or equal t o 27] and mat:hed control subjects who had never been obese. Design: We performed both an individual subject data metaanalysis and a tra ditional meta-analysis. Results: The individual subject data meta-analysis included 124 formerly ob ese and 121 control subjects. RMR adjusted for differences in fat-free mass and fat mass was 2.9% lower in formerly obese subjects than in control sub jects (P = 0.09). A low relative RMR (>1 SD below the mean of the control g roup) was found in 3.3% of the control subjects and in 15.3% of the formerl y obese subjects [difference: 12% (95% CI: 4.7%, 19.3%); P < 0.003]. The tr aditional meta-analysis was based on 12 studies (including 94 formerly obes e and 99 control subjects) and included 3 studies not represented in the in dividual subject data analysis. In this analysis, relative RMR was lower in the formerly obese group than in the control group by 5.1% (95% CI: 1.7%, 8.6%). Conclusions: Formerly obese subjects had a 3-5% lower mean relative RMR: th an control subjects; the difference could be explained by a low RMR being m ore frequent among the formerly obese subjects than among the control subje cts. Whether the cause of the low RMR is genetic or acquired, the existence of a low RMR is likely to contribute to the high rate of weight regain in formerly obese persons.