Obesity Epidemiology

380 EPIDEMIOLOGIC STUDIES OF DETERMINANTS OF OBESITYTable 18.2 continuedStudyPopulationVogels 29 men and(2005) 10 62 womenaged 18-65 yLuke(2006) 9 352 men and392 womenaged 45.9 ±16.1 y fromNigeriaYears ofFollow-upAt least2 y aftercompleting aweight lossprogramAdjustedCovariatesFat-freemass5.5 y Age, sex,fat-freemass, andfat massMain ResultsBaseline RMR was associatedwith percent weight regain(r = –.38, P = .01). Otherpredictors of weight maintenanceafter weight loss were anincrease in dietary restraintduring weight loss and arelatively high baseline fat mass.A significant positive associationwas observed betweenbaseline RMR and weightchange. In stratified analyses,the association was seen amongthose who gained weight but notamong those who lost weight.RMR: resting metabolic rate; RQ: respiratory quotient.weight change. Another might be that the biological relationship between RMR andweight gain is ethnically specific, as indicated by greater susceptibility to obesity inPima Indians compared with other ethnic groups. The Pima Indian results are consistentwith the thrifty gene hypothesis: that metabolic efficiency confers a survival advantageby conserving energy during times of famine but becomes a liability for obesity in anenergy-abundant environment. 12 However, it is unclear why such a biological mechanismwould operate in Pima Indians but not in the Nigerian population. Although both populationshave historically experienced periods of energy scarcity, the majority of theNigerian population has never been exposed to an energy-abundant environment, whichmay potentially explain divergent findings.Studies comparing RMR in formerly obese subjects with never-obese subjects havealso yielded mixed results. In a meta-analysis of 121 formerly obese and 121 controlsubjects, Astrup et al. 13 found that RMR adjusted for differences in fat-free mass andfat mass was 2.9% lower in formerly obese subjects than in matched controls (P = .09).Leibel et al. 14 reported a significant reduction in total energy expenditure and RMR informerly overweight subjects after loss of 10% of initial body weight compared withweight-maintainers who had never been obese. However, in a study among participantsin the National Weight Control Registry, Wyatt et al. 15 found no significant differencein RMR between 40 formerly obese subjects who had maintained weight loss for morethan 1 year and 46 weight-matched controls. Weinsier et al. 16 also demonstrated that inenergy-balanced conditions, there was no significant difference in RMR between weightreducedwomen and never-overweight controls. These findings cast doubt on the setpointtheory, which postulates that those who have lost weight are prone to weight regainbecause of adaptive downregulation in RMR. 17Several cross-sectional studies have reported lower RMR in African Americans thanin Caucasians. For example, Forman et al. 18 found that after adjusting for body weightand lean body mass, African American women had 12% lower RMR than Caucasianwomen. After adjusting for age, Tanner stage, fat mass, and lean body mass, Sun et al. 19likewise found a significantly lower RMR in African American children than in white