A definition to start:
"Personality traits can be defined as stable, fundamental dimensions of personality, influencing our thoughts and behaviours in a variety of situations. According to this definition personality may, at least partly, be related to lifestyle and eating behaviour, and therefore also to obesity."
Purpose:
"The primary purpose of this study was to assess the personality profile of people seeking treatment for their severe obesity and to determine whether they differed from a reference group. The relation between personality and obesity can be viewed in three possible ways; personality predisposes for overeating and/or a physically inactive life-style resulting in weight gain; being obese in itself may have an effect on personality; as an interaction between personality and situation, i.e. a combination of these two mechanisms."
The results:
"On a group level statistical significance was observed on all personality traits, except Psychic Anxiety and Monotony Avoidance for men. Thus, the obese were characterised as more anxiety prone, impulsive, and irritable than the reference group. However, statistical significance is highly dependent on sample size. Effect size statistics, on the other hand, are not and they have a consistent measurement interpretation (trivial, small, moderate and large), thereby providing a standardised context for interpreting meaningful results. Effects size calculations gave a more nuanced picture of our results. Differences between the obese and the reference group were translated as trivial, in effects size terms, regarding Monotony Avoidance and Psychic Anxiety (men only), and small or moderate regarding Somatic Anxiety, Muscular Tension, Psychastenia, Psychic Anxiety (women only), Impulsiveness and Irritability. No differences were large."
"Psychic Anxiety concerns mental issues such as social anxiety, insecurity, and worrying. A small difference was noted between the obese women and women from the reference group, mainly explained by items related to self-esteem. Being obese is a more stigmatised condition for women, which might explain the lack of elevated levels for obese men. Additionally, because of the greater stigma, women may have experienced more dieting failures, which in turn might increase anxiety."
"Small to moderate differences were found regarding Impulsiveness and Irritability. These results are in line with e.g. Fassino et al who describe the obese as more impulsive and irascible than normal weight persons. Such characteristics may reflect irregular eating habits, repeated attempts at losing weight and accompanying relapses. Severely obese seeking treatment are psychologically distressed and it has been proposed that all forms of negative affect contribute to increased aggression. Distress has also been linked to a breakdown of impulse control. Impulse control may involve delayed gratification, while emotional distress may shift priorities to the present aiming at regulating the negative affect. Thus, impulse control and affect regulation clash and priority is given to the short-term goal of feeling better at the expense of impulse control."
"When we looked closer at obese persons from the reference group some intriguing results were found. They did not differ on any scale when compared to the non-obese, and they scored significantly lower on all personality scales (Irritability not significant) compared to the obese patients. These results indicate that obese individuals not seeking treatment have the same personality profile as normal- or overweight persons. Thus, obesity per se may not differentiate these groups but rather whether or not they seek treatment. Since the obese in the reference group were less over-weight and had a greater portion of men, these results should be interpreted with some caution. However, they are in line with previous studies showing heterogeneity of the obese population. For example, those seeking treatment report higher levels of distress compared to those not seeking treatment. Differences have also been noted between patients who prefer more drastic weight-reduction methods, such as surgery or appetite depressants compared to patients who prefer conventional treatment."
"Costa et al proposed several possible explanations in an impressive study on more than 23000 persons from 26 cultures. One was that, in countries with more progressive sex role ideologies, men and women may compare themselves with others of both genders, while men and women in more traditional cultures make within-gender comparisons."
Rydén, Anna, et al. "Severe obesity and personality: a comparative controlled study of personality traits." International Journal of Obesity 27.12 (2003): 1534-1540.
"Results: Despite elimination of extreme BMIs, different associations between BMI and EPQ subscales emerged for men and women. Among women, increasing BMI was significantly associated with increased neuroticism and reduced extraversion. Among men, increasing BMI was associated with increased extraversion and psychoticism. In all cases, the magnitude of the association was very small."
[increased extraversion in men was later explained (in a way) by a team from McMaster University in that obesity and happiness were linked to the FTO gene - cultural effects seem to be in play with women. Cf. Costa (above)]
"Discussion: Increasing BMI was associated with potentially poorer adjustment among women but better adjustment among men. These findings are consistent with recent reports and, taken together, suggest that these patterns are not accounted for solely by the extremes of the BMI distribution."
"Among women, greater BMI was associated with increased neuroticism (r = 0.09) and decreased extraversion (r = −0.06; p < 0.0001 in both cases). Among men, greater BMI was associated with increased extraversion (r = 0.07) and psychoticism (r = 0.07; p < 0.0001 in both cases)."
"The relationship between relative body weight and dimensions of personality was distinctly different for men and women in this population-based study from England. This finding is consistent with recent reports in the literature (6, 7) and was observed despite the fact that extreme BMI scores were excluded from analyses. Thus, as Friedman and Brownell (2) intimated, gender seems to be a consistent moderator of BMI–psychological functioning relationships. In contrast, the observed effects were very small. These results suggest that in people who are not too thin or too heavy, variability in BMI has a small association with variability in neuroticism, extraversion, and psychoticism, and this seems to vary by gender. One avenue for future research is to map out causal pathways and underlying mechanisms for these associations. A variety of potential mechanisms, including genetic, physiological, and psychosocial, have been suggested (14). The results of this study caution against haphazardly pooling men and women and suggest the potential benefits of developing gender-specific models when testing mechanisms."
Faith, Myles S., et al. "Gender differences in the relationship between personality dimensions and relative body weight." Obesity Research 9.10 (2001): 647-650.
"Objective: To determine whether, in the general population, individuals in numerous abnormal body weight categories had higher odds of having personality disorders (PDs) than normal-weight individuals. Although personality functioning is hypothesized to be associated with body weight, there is a dearth of empirical evaluation of this topic."
"underweight = BMI < 18.5"
"classified as overweight or obese (defined as a body mass index [BMI] of >= 25)"
"abnormal body weight has also been shown to be associated with a variety of Axis I psychiatric disorders. However, whether body weight is associated with Axis II personality disorders (PDs), another important aspect of mental health, has rarely been investigated."
"For example, a direct causal relationship may exist between some of the behavioral factors linked to cluster A PDs and weight gain in women. The avoidance of social interaction in paranoid and avoidant PDs could potentially lead to a more sedentary lifestyle and subsequent increased rates of overweight and obesity due to a decrease in activities outside of one's home. Behavioral features of antisocial PD could similarly lead to excess adiposity in women. For example, the impulsivity that characterizes antisocial PD may lead to overweight or obesity in this population because the known association of impulsivity with a lack of inhibition with regard to eating may lead to overindulgence and therefore increased body weight."
[Another reason to avoid a person (as a spouse) who has demonstrated impulsivity in other realms (e.g. sexual) - e.g. avoidant ]
"[the] Underweight [group] showed a significant association with schizoid PD in women, and this link may also have a direct causal explanation. For example, the disinterest in social relationships and activities that characterizes schizoid PD may result in fewer opportunities for social eating. Schizoid PD may alternatively share features with clinical or subclinical disordered eating, which may lead these individuals to become underweight. For example, much like individuals with disordered eating habits, individuals with schizoid PD may not eat for pleasure and may become underweight as a result. Because the NESARC did not assess eating disorders, we are unable to determine whether an association of underweight with schizoid PD would remain after eating disorders, such as anorexia nervosa, were taken into account."
"Alternatively, it has been shown that overweight men seem to protect themselves from the negative emotional effects of being overweight that women experience by psychologically distancing themselves from the overweight label. Thus, they do not conceptualize themselves as overweight, and the positive coping strategies that men engage in to combat the stigma they experience in their lives as a result of being overweight"
[See Costa remark above where gender-roles could relate to such emotional effects]
"Results: After adjusting for sociodemographics, Axis I disorders, schizophrenia, physical health conditions, and comorbid PDs, extreme obesity was associated with antisocial or avoidant PDs (adjusted odds ratio (AOR) range = 1.66–1.73), whereas underweight was associated with increased odds of schizoid PD (AOR = 1.89). The pattern of associations differed when stratified by gender. Overweight men had lower odds of paranoid PD (AOR = 0.73). Women with higher-than-normal body weights had higher odds of paranoid, antisocial, and avoidant PDs (AOR range = 1.33–2.50), whereas underweight women more often met the criteria for schizoid PD (AOR = 1.95)."
[In general, higher rates of Cluster A, B, C PDs in obese people, but also antisocial and avoidant PDs in obese women. It should be noted that avoidant PDs are associated with higher than average sexual partner counts in women.]
Mather, Amber A., et al. "Associations between body weight and personality disorders in a nationally representative sample." Psychosomatic medicine 70.9 (2008): 1012-1019.
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