A large-scale longitudinal study examined the association between personality traits and body weight over time. The results showed that future body mass index (BMI) cannot be predicted based on personality traits, but future changes of personality traits of consciousness and agreeableness could be predicted based on BMI values. The study was published in the Journal of Personality.
Personality traits are psychological characteristics that influence an individual’s behavior, motivation, thoughts, and emotions across various situations. They are relatively stable and consistent, allowing researchers to categorize and describe individual differences in personality. The most widely accepted concept of personality, the Big Five personality model, proposes that humans have 5 broad personality traits. These traits are neuroticism, extraversion, openness for experience, agreeableness and conscientiousness.
Multiple studies have demonstrated that personality traits are weakly associated with various physical health indicators. To some extent, they can predict the onset of multiple common diseases. Additionally, there appears to be an association between personality traits and body mass index, a health indicator calculated by dividing one’s weight by the square of their height.
Study author Kadri Arumäe and her colleagues noted that previous studies did not clarify the nature of the link between body mass index and personality. Does one’s body mass influence personality or is it personality traits that influence one’s body mass? Is it some other factor influencing both? They conducted a study to examine this.
These researchers based their study on the reasoning that cause-and-effect relations cannot run backwards in time. If one factor causes another, using the cause to predict future values of the effect should yield more successful predictions than using it to predict past values of the effect. In this way, they could calculate strengths of associations between past and future values of body mass index and personality and infer which is likely to be the cause and which to be the consequence.
The study authors analyzed data from the Wisconsin Longitudinal Study, which followed a sample of 10,317 individuals who graduated from Wisconsin high schools in 1957, most born in 1939. They used data collected at three points: 1993-1994, 2004-2005, and 2011, focusing on participants’ BMI values and Big Five personality traits.
The results indicated a very weak association between personality traits and BMI measured at the same time point. However, personality traits at one time point did not correlate with future BMI values. While a statistical model could predict future BMI values using responses to individual personality inventory items, it found no correlation with measures of personality traits.
Neither personality traits nor individual answers to personality assessment statements could predict changes in body mass index. However, body mass index could predict future changes in the personality traits of conscientiousness and agreeableness. Individuals with lower body mass index values (i.e., lower body weight for their height) tended to a tiny bit more conscientious and agreeable on average compared to those with higher body mass index values.
Conscientiousness is a personality trait characterized by the tendency to be organized, responsible, goal-oriented, and reliable, often associated with being diligent, punctual, and detail-oriented in one’s actions and work. Agreeableness, on the other hand, is a personality trait reflecting a person’s proclivity to be cooperative, kind, empathetic, and generally pleasant to be around. Agreeable individuals emphasize harmonious social interactions and a willingness to compromise in relationships.
“In sum, we found that body mass index had within-person correlations with Agreeableness, Conscientiousness, and several personality items and that it also predicted changes in the same traits in a large sample of adults over time intervals of about 7 to 11 years,” the study authors concluded. “The associations were consistent with causal influences of body mass index on these personality traits, suggesting that either body weight or health status more generally may influence them. Body mass index may thus be among the currently poorly understood correlates of personality development. In contrast, although personality traits were collectively able to predict future body mass index, no clear support was found for causal influences of personality traits on body mass index.”
The study sheds light on the likely nature of the links between body weight and personality. However, it should be noted that the reported associations were very, very weak, practically negligible. They were only detectable because the analyses were done on an extremely large sample of people.
The study, “Body mass predicts personality development across 18 years in middle to older adulthood”, was authored by Kadri Arumäe, René Mõttus, and Uku Vainik.
