Background/Objectives: Many personality traits correlate with BMI, but the existence and direction of causal links between them are unclear. If personality influences BMI, knowing this causal direction could inform weight management strategies. Knowing that BMI instead influences personality would contribute to a better understanding of the mechanisms of personality development and the possible psychological effects of weight change. We tested the existence and direction of causal links between BMI and personality.Subjects/Methods: We employed two genetically informed methods. In Mendelian randomization, allele scores were calculated to summarize genetic propensity for the personality traits Neuroticism, Worry, and Depressive Affect and used to predict BMI in an independent sample (N=3 541). Similarly, an allele score for BMI was used to predict eating-specific and domain-general phenotypic personality scores (PPSs; aggregate scores of personality traits weighted by BMI). In a Direction of Causation analysis, twin data from five countries (N=5 424) were used to assess the fit of four alternative models: PPSs influencing BMI, BMI influencing PPSs, reciprocal causation, and no causation.Results: In Mendelian randomization, the allele score for BMI predicted domain-general (β=0.05; 95% CI 0.02, 0.08; P=.003) and eating-specific PPS (β=0.06; 95% CI 0.03, 0.09; P<.001). The allele score for Worry also predicted BMI (β=-0.05; 95% CI -0.08, -0.02; P<.001), while those for Neuroticism and Depressive Affect did not (P≥.459). In Direction of Causation, BMI similarly predicted domain-general (β=0.21; 95% CI 0.18, 0.24; P<.001) and eatingspecific personality traits (β=0.19; 95% CI 0.16, 0.22; P<.001), suggesting causality from BMI to personality traits. In exploratory analyses, links between BMI and domain-general personality 2 CAUSALITY BETWEEN BMI AND PERSONALITY traits appeared reciprocal for higher-weight individuals (BMI>~25). Conclusions:Although both genetic analyses suggested an influence of BMI on personality traits, it is not yet known if weight management interventions could influence personality.Personality traits may influence BMI in turn, but effects in this direction appeared weaker.

Food reward is an important concept for research in eating behaviors. Many food reward tasks have been developed and are in active use. However, little is known how much these tasks overlap. Here, we sought to compare three promising food reward tasks: (1) the Leeds Food Preference Questionnaire (LFPQ; a procedure combining explicit ratings of wanting and liking and an implicit wanting task based on forced choice), (2) a hand grip force task, and (3) an emotional attentional blink (EAB) task. Specifically, we assessed whether the tasks are sensitive to changes in hunger, correlate with each other, and correlate with trait binge eating and snack food calorie intake. Thirty-nine women aged 25.51 ± 5.99 years, with a BMI of 22.51 ± 3.58 kg/m 2 completed the three tasks twice: after a 6-h fast and following a breakfast meal. In the fasted condition, participants were also given ad libitum access to snack foods to assess calorie intake. Prior to the two laboratory sessions, participants completed a trait binge eating questionnaire. Results revealed that the LFPQ’s explicit wanting and explicit liking subscales, as well as grip force reflected higher food reward scores in the fasted condition. The three metrics also correlated positively with each other. Explicit wanting and liking correlated with snack food intake, while grip force did not. None of the tasks were related to trait binge eating. Reaction times in the forced choice procedure did not reflect changes in hunger, but the task was nevertheless able to differentiate between foods varying in taste and fat content. The EAB was not sensitive to the hunger manipulation; neither did the task correlate with binge eating or energy intake. Collectively, our findings suggest that the explicit wanting and liking scales and the grip force task measure the same construct, whereas EAB results may be obscured by a variety of potential confounding factors. Future research could include additional food reward tasks in comparisons, measure covariates that may moderate the variables’ associations, and compare hunger-dependent changes in food reward in different subgroups.

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Importance: Many personality traits robustly correlate with BMI, but the existence and direction of causality are unclear. As personality traits also correlate with various other mental and physical health outcomes, understanding causality in these intersections is widely useful; understanding causality between BMI and personality specifically could inform weight management strategies (if personality influences BMI) or delineate mechanisms of personality development (if otherwise).Objective: To test the existence and direction of causal links between BMI and personality.Design: Two genetically informed analyses. In Mendelian randomization, an allele score for BMI was used to predict eating-specific and domain-general phenotypic personality scores, and allele scores for personality traits were used to predict phenotypic BMI. In Direction of Causation, twin data were used to infer the best-fitting causal model (personality influencing BMI, BMI influencing personality, reciprocal causation, or no causation).Setting: Cross-sectional data: molecular genetic data for Mendelian randomization, twin data for Direction of Causation.Participants: Mendelian randomization used Estonian Biobank data (N=3,541); Direction of Causation combined twin samples from five countries (N=5,424).Exposures: In Mendelian randomization, genetic propensity for BMI and the personality traits Neuroticism, Worry, and Depressive Affect was summarized in allele scores. In Direction of Causation, phenotypic BMI and phenotypic personality scores were treated as both exposures and outcomes. Phenotypic scores for domain-general and eating-specific personality were calculated by summing relevant questionnaire items weighted by their empirical association with BMI, maximizing statistical power.Main outcomes and measures: Phenotypic BMI and phenotypic personality scores.Results: The allele score for BMI predicted domain-general (β=0.05, 95% CI 0.01–0.08, P=.009) and eating-specific phenotypic personality score (β=0.05, 95% CI 0.01–0.08, P=.009). The allele score for Worry also predicted BMI (β=-0.07, 95% CI -0.10–-0.03, P&lt;.001), while those for Neuroticism and Depressive Affect did not (P≥.358). In Direction of Causation, BMI similarly predicted domain-general (β=0.21, 95% CI 0.18–0.24, P&lt;.001) and eating-specific personality (β=0.19, 95% CI 0.16–0.22, P&lt;.001). In exploratory analyses, causal links between BMI and domain-general personality traits appeared reciprocal for higher-weight individuals (BMI&gt;~25).Conclusions and Relevance: Results suggest an influence of BMI on personality. Maintaining or achieving normal-range weight may contribute to a more favorable personality profile, possibly relevant in mental health and general well-being.Supplement: Supplementary online content available at https://osf.io/meqxn/

Various personality domains and facets correlate with body mass index (BMI), but recent studies suggest that using narrower personality traits—nuances—could contribute to a more detailed understanding of personality–body weight associations. We used three large datasets with different inventories to describe nuances’ correlations with BMI and explore whether BMI predominantly correlated with affective, behavioral, cognitive, or motivational item content. BMI correlated with many nuances, most prominently those reflecting immoderation, lack of orderliness, talkativeness, leadership tendencies, anger, traditionalism, and preference for routine. The highest nuance-level correlation was .21, compared to .11 for the Five-Factor Model domains. BMI correlated most strongly with nuances predominantly reflecting behaviors. Nuance-based approaches can thus reveal the strength, multitude, and content-nature of personality–outcome correlations that can potentially remain hidden in broader traits. If personality traits become relevant in the prevention or treatment of obesity, a focus on narrow behavioral traits may be especially warranted.