Finally, we found little evidence that weight contributes to changes in personality across adulthood. BMI was unrelated to change in the five broad traits over time and only one effect emerged at the facet level: Participants with higher BMI declined more on N5: Impulsiveness over time. This association likely reflects regression to the mean in that the heaviest participants were also the most impulsive. Thus, over time, these participants’ impulsivity scores declined the most. The lack of significant effect of weight on personality change may be due to the high level of trait stability in this adult sample, with intra-individual variability accounting for less than 15% of the variance (Terracciano et al., 2005). Further, after accounting for transient error (Chmielewski & Watson, 2009), there may be little remaining variance to be explained by other factors. Research on adolescents and young adults, a time when personality is less stable, may be more fruitful for testing how weight may shape personality traits over time.
