A twin study of the relation between age at dieting onset and to adult BMI and dieting behaviors
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Background: The association between dieting behaviors and weight gain has been well documented in numerous studies. However, there is an ongoing debate whether individuals who are predisposed to a greater BMI are less likely to successfully diet, or if dieting behaviors result in a greater BMI. Moreover, an early age at dieting onset may be a particular risk factor for higher adult BMI and risky dieting behaviors. Methods: Female twins ages 18-60 years (N=950) from the University of Washington Twin Registry completed a survey in 2006. A subsequent follow-up survey was completed approximately 3-years later. Overall and within-twin pair analyses, which included all twin participants and statistically accounted for twin's relatedness, were conducted in order to quantify associations between the age at dieting onset and 1) BMI at time of baseline assessment, 2) change in BMI between two surveys, and 3) risky eating behaviors. Results: Overall, in adjusted models significant associations were found between an earlier age at dieting onset and BMI at baseline (p=.003), and with use of dieting methods such as restrained eating (p<0.001), risky dieting behaviors (p=0.016), and weight cycling (p=0.011). However, in within-pair models that adjusted for shared genetic and family environment factors, there were no significant associations between age at dieting onset and any of the above measures. Conclusion: Among adult female twins, an earlier age at dieting onset was associated with an increased BMI, and greater use of dieting behaviors including restraint, risky dieting methods, and weight cycling in overall, cross-sectional analyses. However, when genetic and family environment factors were accounted for using within-twin pair analyses, the above associations were no longer significant. Thus, genetics and the family environment may influence both the age at dieting onset and BMI, as well as the adoption of risky eating behaviors.
- Nutritional sciences