Body mass predicts personality development across 18 years in middle to older adulthood

Abstract

Various personality traits have longitudinal relations with body mass index (BMI), a measure of body weight and a risk factor for numerous health concerns, but causality in and direction of these associations is unclear. Using three waves of the Wisconsin Longitudinal Study (N = 12,235, mean age = 53.33 at baseline), we tested bidirectional longitudinal associations between BMI and the Five-Factor Model personality domains and their items and assessed the associations’ compatibility with causal influences using within-person correlations. In elastic net models, the five domains predicted concurrent BMI with an accuracy of r = .08 but were unable to predict future BMI. In contrast, 29 personality items predicted concurrent and future BMI at r = .21 and r = .16 to .25, respectively, supporting the predictive utility of nuanced trait measurements. In multilevel models, BMI had within-person correlations with Conscientiousness, Agreeableness, and several items; time-invariant third factors like genetics or childhood environments therefore could not (fully) account for their relations. BMI predicted future changes in these same personality traits (|b*| = .03 to .08), but no trait predicted subsequent changes in BMI. In sum, body weight may contribute to adults’ personality development, but the reverse appears less likely.