Rationale: Past research has shown that personality traits relate to body weight, but this relationship may be confounded by unobserved family-level characteristics such as genetic endowments.
Objective: The purpose of this study was to investigate whether the association between personality traits, as measured by the Big Five taxonomy, and body weight among young adults is spurious owing to shared family background.
Methods: Participants were drawn from the full (n = 14,366) and family (n = 2813) samples of the National Longitudinal Study of Adolescent to Adult Health (Add Health). The study employed family-fixed effects to eliminate shared family background factors that might affect personality traits and body weight simultaneously.
Results: Among the Big Five personality traits, only conscientiousness showed a robust association with body weight, including body mass index (BMI) and obesity risk. These results were robust to adjustments for family-fixed effects, which indicates that the association between conscientiousness and body weight is generally not confounded by unobserved family-level characteristics shared by siblings. A one-standard-deviation increase in conscientiousness was associated with a decrease in BMI by 0.89 (equivalent to a 2.5 kg decrease in weight for an individual with an average height of the sample) and a 12% reduction in the probability of being obese. This study also found some suggestive evidence of gender and racial/ethnic differences. The association between conscientiousness and obesity was larger and statistically significant only for women, and conscientiousness was most strongly associated with obesity among Hispanic people.
Conclusion: Conscientiousness is associated with decreased body weight net of unobserved background characteristics that are shared by siblings. The results suggest that interventions that develop personality traits may have "spillover effects"; in other words, they may also help reduce obesity.
Keywords: Big-Five; Body mass index; Obesity; Personality.
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