Two genetic analyses to elucidate causality between body mass index and personality

Abstract

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.

Triangulating Causality Between Childhood Obesity and Neurobehavior: Twin and Longitudinal Evidence

“…Personality/psychopathology and cognitive test results can be compromised by intrapersonal components like response bias or motivation which are irrelevant for the directly observed measures of childhood obesity and brain morphology. At the same time, previous analyses showed that explicitly modeling reliability did not change DoC conclusions 27 . Future studies using different causal inference methods should build complementary evidence 27 .…”

“…At the same time, previous analyses showed that explicitly modeling reliability did not change DoC conclusions 27 . Future studies using different causal inference methods should build complementary evidence 27 .…”

“…However, it is unclear if obesity may have causal associations with these neurobehavioral domains and aspects of brain morphology and, if so, what the direction of these associations may be. A recent study in adults showed that neurobehavioral correlates of obesity are largely heritable (Vainik et al, 2018) and follow-up genetic analyses with two different methods suggest that obesity may cause variance in personality traits (Arumäe et al, 2021). In childhood, obesity is assumed to be causally influenced by eating, lifestyle, and socio-cultural behaviors and to have causal effects on cognitive abilities (Sahoo et al, 2015) and brain morphology (Alosco et al, 2014; Prats-Soteras et al, 2020).…”

Beyond BMI: Personality Traits’ Associations With Adiposity and Metabolic Rate

“…However, the current results still suggest that the magnitude of the correlations may be underestimated when using BMI. In sum, if the personality profile of adiposity is thought of as a collection of behavioural symptoms that accompany obesity (Arumäe et al, 2021), then applying RFM has shown us that these behavioural symptoms are more pronounced than previously thought. This could be a positive signal for weight loss interventions to consider personality traits as their associations with overweight may be stronger than has been thought.…”

“…But the associations may also run in reverse, as suggested by longitudinal studies (Lahti et al, 2013). Causal influences have been theorized to be bidirectional (Sutin & Terracciano, 2017), and genetic analyses have supported this view (Arumäe et al, 2021). Therefore, although the correlations might also arise from common causes (Sutin et al, 2013;Nagel et al, 2018;Vainik et al, 2018), the longitudinal and genetic analyses suggest that causal associations may instead (or additionally) exist.…”