Body weight is a fundamental individual difference variable that has a pervasive effect on nearly every aspect of our lives. Although most commonly implicated in physical health, adiposity contributes to a variety of psychological processes, such as well-being, identity formation, and person perception. Overweight individuals are prone to depression (
Luppino et al., 2010), have poor body image (
Schwartz & Brownell, 2004), are evaluated negatively by others (
Crandall, 1994), and are ascribed traits based on their body size (
Roehling, Roehling, & Odland, 2008). In fact, just being associated with someone who is overweight can lead to negative evaluations (
Hebl & Mannix, 2003). As such, body weight contributes to how we understand ourselves, how we see others, and how others see us.
Weight and weight gain are certainly multiply determined. Adiposity varies as a function of age, sex, and socioeconomic status (
Ogden et al., 2006;
Yach et al., 2006), and, genetically, the fat mass and obesity associated (
FTO) gene has been consistently associated with BMI (
Frayling et al., 2007;
Scuteri et al., 2007). In addition to these demographic and genetic influences, psychological processes contribute to an individual’s waistline. Eating can be a form of emotion regulation (
Evers, Stok, & de Ridder, 2010), the inability to resist cravings contributes to binge eating (
Rush, Becker, & Curry, 2009), whereas self-discipline is required to exercise regularly (
Hoyt, Rhodes, Hausenblas, & Giacobbi, 2009). This line of evidence suggests that weight is a physical manifestation of processes inherent to an individual’s characteristic ways of thinking, feeling, and behaving. Thus, body weight is, in part, a reflection of the processes that define common personality traits.
The traits within the Five-Factor Model (FFM) of personality, Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness, have been linked to health behaviors and outcomes in general (
Friedman, 2008;
Goodwin & Friedman, 2006;
Ozer & Benet-Martínez, 2006) and to abnormal weight in particular (
Brummett et al., 2006;
Chapman, Fiscella, Duberstein, Coletta, & Kawachi, 2009;
Terracciano et al., 2009). Of the five traits, Conscientiousness is the most consistently associated with adiposity. Across different personality measures, populations, and both self-reported and clinician-assessed weight, conscientious individuals have lower adiposity (
Brummett et al., 2006;
Chapman et al., 2009;
Roehling et al., 2008;
Sullivan, Cloninger, Przybeck, & Klein, 2007;
Terracciano et al., 2009). In particular, the order and self-discipline facets of Conscientiousness are strongly associated with weight (
Terracciano et al., 2009). Presumably, those who score higher on Order and Self-Discipline are leaner because they are organized and stick to their diet and meal schedule. The lifestyle choices of individuals high in Conscientiousness likely contribute to their healthy weight. These individuals, for example, are physically active (
Rhodes & Smith, 2006), restrain from binge eating and drinking (
Rush et al., 2009), and are less likely to have disordered eating (
Bogg & Roberts, 2004).
Abnormal weight has also been associated with trait Neuroticism. Individuals who are underweight tend to score higher in proneness to negative affect than those who are in the normal weight range (
Kakizaki et al., 2008;
Terracciano et al., 2009). Similarly, in clinical populations, underweight individuals and those with eating disorders tend to score higher in Neuroticism (
Bulik et al., 2006;
Cassin & Von Ranson, 2005). On the other side of the BMI continuum, overweight and obese groups tend to have a higher prevalence of psychiatric disorders (
Petry, Barry, Pietrzak, & Wagner, 2008), which suggests that such groups may also score higher on Neuroticism. Neuroticism may be associated with both ends of abnormal weight for at least two reasons: There could be a curvilinear relation between weight and Neuroticism, such that both ends of the BMI continuum are associated with higher Neuroticism and/or different aspects of Neuroticism may be associated with being overweight or underweight (see below).
There is less evidence for the association between BMI and the remaining three traits. Among Japanese participants, overweight groups scored lower on Extraversion (
Kakizaki et al., 2008), whereas no association was found among Italians (
Terracciano et al., 2009) or Americans (
Chapman et al., 2009). Some have found this negative association between Extraversion and BMI among women, but the opposite among men (
Faith, Flint, Fairburn, Goodwin, & Allison, 2001). Among men, higher Agreeableness has been associated with higher BMI (
Chapman et al., 2009), but others have found the opposite (
Brummett et al., 2006). Studies that have included a measure of Openness have either found a negative (
Brummett et al., 2006) or no (
Chapman et al., 2009;
Terracciano et al., 2009) relation with BMI.
These seemingly inconsistent findings may be due, in part, to the use of different personality measures that emphasize different facets of the traits. For example, scales that tap into the more impulsive aspects of Neuroticism may be more strongly related to higher BMI, whereas scales that tap into the vulnerability aspects of this trait may be related to lower BMI. Similarly, individuals who score high on scales that emphasize the activity component of Extraversion may weigh less, whereas individuals who score high on scales that emphasize the positive emotionality components of Extraversion may weigh more. As such, it is necessary to have a detailed personality assessment that measures both the broad and narrow traits to be able to identify which aspects of personality traits are associated with abnormal weight.