The Relationship Between Personality and Obesity
Abstract
Obesity is a worldwide medical condition that has been continuously increasing in scale and has been linked to various life-threatening diseases and conditions. The research aim of this paper is to investigate possible connections between obesity, weight gain, and personality traits as well as to compare different study designs to observe changes over time. It is important for both achieving more accurate findings, and for knowing how to design an ideal obesity treatment program that would make the best possible interventions from a developmental standpoint. Therefore, this literature review summarizes five studies on the relationship between obesity and personality traits that have taken either cross-sectional and/or longitudinal approaches based on different sample sizes with similar objectives, which was to assess the potential association between personality traits and obesity to make a better understanding, therefore, develop new treatment methods and health interventions that are more suited to people with different personality traits who are coping with obesity or who are trying to prevent weight gain. Most cross-sectional studies find links between the Big-Five Personality Traits and obesity while longitudinal studies -which are not as common as the cross-sectional ones- manage to find fewer links. The longitudinal results were only congruent with the associations with the agreeableness trait, which indicates that agreeableness is inversely associated with becoming obese. It is important to note that all the studies reviewed here agree that age and sex are not significant determinants in the relationship between obesity and personality. Nevertheless, personalized health interventions and treatment strategies are advised with divergences between the two study designs in mind.
Most cross-sectional studies find links between the Big-Five Personality Traits and obesity.
Introduction
The main indicator of obesity in all the studies is the Body Mass Index. The adult BMI score of 30 and over is considered obese by the Centers for Disease Control and Prevention, the national public health agency of the United States (Centers for Disease Control and Prevention, 2021).
One of the most broadly accepted inventories of personality traits is the Big-Five Personality Traits. It consists of the following scales/constructs: neuroticism, openness to experience, conscientiousness, extraversion, and agreeableness (Goldberg, 1981). Although most studies have adopted the Big-Five questionnaire in one form or another when it comes to assessing personality traits, there is one study in this summary that has taken the long way of adopting a less common measure, the Temperament and Character Inventory, reasoning that its assessment of personality variations is reproducible (Sullivan et al., 2007). However, some of its items are somewhat equivalent to the Big-Five items which makes the results of these studies comparable. People with a high novelty-seeking temperament tend to be impulsive and avoid monotony. In this sense, it closely relates to the openness to experience trait in the Big-Five as it is described as generally open with a vivid imagination, enjoying new activities, and in a high need for variety in life. Low levels of reward dependence correlate with being rather practical, cold, withdrawn, and independent. It resembles scoring low on the extraversion trait and having a formal and distant nature in social relationships. Likewise, self-directedness and persistence are similar to the conscientiousness of the Big-Five inventory. Cooperativeness on the other hand finds its form in the Big-Five inventory as the agreeableness trait.
Review
Obesity is excessive fat accumulation in one’s body which is classified by the Body-Mass Index (BMI) score of 30 and over. It is a major risk factor for non-communicable diseases such as diabetes, cardiovascular diseases, musculoskeletal disorders, and various cancer types (Webber et al., 2012). Worldwide obesity has nearly tripled since 1975, being prevalent initially in high-income countries and increasingly getting more prevalent in middle- and low-income countries. According to World Health Organization (WHO), more than 1.9 billion adults around the globe were obese by 2016. When considering its consequences, it is important to seek more effective ways of treatment and new preventive measures. Therefore, it is equally important to assess the possible relationship between personality traits which may lead to new findings that would increase treatment success and potentially increase the life quality of people with obesity. A study by Sullivan et al., (2007) had three groups of participants: lean (BMI < 25), general obese, and obese who underwent a comprehensive weight loss program. All Temperament and Character Inventory (TCI) factors being converted to the Big-Five Inventory factors, people with obesity were more open to experience, and less conscientious compared to lean subjects. Comparing the participants of the weight loss program to the general obese population, they were more extroverted and tended to be more agreeable. Successful attempts of losing weight resulted in less openness to experience. Therefore, high scores in openness to experience (originally novelty-seeking) are related to decreased success in achieving behavioral therapy-induced weight loss (Sullivan et al., 2007).
Another study with a less diverse sample that only included obese women was conducted in Canada (Provencher et al., 2008). None of the 154 participants were trying to lose weight so they were in their natural states in dietary terms, but they were preoccupied with their weight and eating as shown by the psychological functioning questionnaire (Beck Depression Inventory).¹ Additionally, they directly implemented the NEO Five-Factor Inventory (NEO-FFI) to capture the five dimensions of personality as well as the Three-Factor Eating Questionnaire (TFEQ) to measure cognitive dietary restraint, disinhibition, and susceptibility to hunger. After regression analysis, they found neuroticism to be associated with cognitive dietary restraint, disinhibition, and susceptibility to hunger, while there was a negative association between agreeableness and susceptibility to hunger. Conscientiousness was found to be a positive determinant of dietary restraint and was also linked to BMI as opposed to the previous study from Sullivan et al., (2007). This suggests that higher levels of conscientiousness might be necessary to limit one’s appetite.
Researchers from Texas A&M University used a dataset from Karolinska University Hospital, Sweden that was collected between 2003–2005 which consisted of 442 obese participants (282 women, 160 men). NEO Big-Five Personality Inventory (NEO PI-R) was used alongside Dutch Eating Behavior Questionnaire (DEBQ) to see how the three eating types (emotional eating, external eating, restrained eating) are related to personality characteristics and what it takes to restrain emotional and external eating. Correlation analysis between DEBQ and NEO PI-R results showed that the link between neuroticism and emotional and external eating types is highly significant, the impulsiveness facet of neuroticism being the most correlating facet among emotional and external eaters. Conscientiousness was also correlated with emotional eating. On the flip side, restrained eating was also significantly correlated to conscientiousness, achievement striving, and self-discipline showing the most correlation.²
The remaining two studies adopt both cross-sectional and longitudinal study designs and observe if previous findings stay valid when the time element enters the equation. A study from Magee and Heaven, (2011) aims to find possible associations between personality characteristics and weight gain and obesity by comparing data before 2-year weight gain and after 2-year weight gain. It uses data collected for Household, Income and Labour Dynamics in Australia (HILDA) Survey (2005–2008). HILDA is a comprehensive survey that employs both in-person interviews and self-reports to gather social, medical, and psychological data from its participants. Potential artifacts were also considered such as physical activity and alcohol consumption.³ This gives a better insight into what role personality characteristics play in obesity and weight gain. This data was collected in 6 waves, 3 of which are used in the research. They had 5265 Australian adult participants, 52.6% of whom were female and not all participants were obese. For assessing personality characteristics, 36-item Goldberg’s Big Five Markers Scale is used. Cross-sectional results indicate that conscientiousness is negatively associated with obesity while neuroticism, agreeableness, and extraversion are positively associated with obesity. Longitudinal results of the study indicate that only the extraversion trait is significantly associated with weight loss and weight gain.
The biggest data sample, the longest duration in data collection, and recentness featured in the present literature is the study of Bagnjuk et al., 2019. They employed the German Socio-Economic Panel (GSOEP) data collected in waves from 2005 to 2013. It resembles the previous study as it also featured social and demographic data from a large sample. The present study had more than 20.000 participants over 8 years and used 18.291 observations in their cross-sectional analysis and 2026 observations in the longitudinal part. The employment of a longitudinal data set is reasoned in observing the change from non-obese to obese state.⁴ They used the BFI-S inventory of the Big-Five questionnaire which is a self-report scale. Their results indicate that the results between the cross-sectional and longitudinal analyses are inconsistent.⁵ After adjusting the confounders, the cross-sectional results showed significant associations between obesity and conscientiousness, extraversion, openness to experience, agreeableness. However, the longitudinal results were only congruent with the associations with the agreeableness trait, which indicates that agreeableness is inversely associated with becoming obese.
It is important to note that all the studies reviewed here agree that age and sex are not significant determinants in the relationship between obesity and personality, except Bagnjuk et al., 2019 study states that high neuroticism is a risk of obesity for women, and age is significantly associated with obesity risk.⁶ Although, after separately conducting interaction analyses for both genders, they observed no significant associations between personality traits and gender.⁷
Age and sex are not significant determinants in the relationship between obesity and personality.
These results indicate that the common element of the cross-sectional studies reviewed here is conscientiousness being inversely associated with obesity, and positively linked to dietary restraint. This shows that high conscientiousness may be an important factor for successful weight loss. Therefore, treatments that aim to pave the way for helping patients increase their conscientiousness would be helpful for people with obesity to lose weight. Longitudinal results, on the other hand, show a similar inverse relationship between agreeableness and obesity. As a result, it may be concluded that increasing the agreeableness trait of a person with obesity will increase the treatment success.
Obesity is a major risk factor for non-communicable diseases such as diabetes, cardiovascular diseases, musculoskeletal disorders, and various cancer types (Webber et al., 2012).
Discussion
Although every study has its strengths and weaknesses, most cross-sectional studies provide similar results because of the constant data that does not reflect change over long periods. Reviewed studies show that results differ once a study adds the time dimension and becomes longitudinal. The main difference is that the cross-sectional studies do not factor in developmental changes of individuals, or their socio-economic conditions over time which leads to making it relatively easier to reason obesity and weight management success in personality traits which are, by design, the only set of variables for obesity to be correlated to. Although this is not to deny the findings of the studies reviewed here, longitudinal studies that observe the participants periodically have the edge over cross-sectional studies since both personality traits and one’s weight are not static variables. Therefore, future studies need to factor in that personality traits are amenable in the long term as the personality is under constant development during one’s lifespan.
Another factor studies come in short is the method of data collection. Most studies rely on self-report questionnaires, and while self-report is useful in the form of personality questionnaires, it might not be always as sufficient when it comes to measuring dietary habits.⁸
Perception of obesity in the general population might differ from country to country both because obesity rates between countries can be vastly different (i.e., India vs. the USA)⁹, and because the cultural understanding and acceptance of body weight between cultures are also different. Public pressure, societal expectations, and physical conditions that obese people face might easily vary between countries, as well, which can shape or alter their personalities in the long run. Therefore, being obese is not an umbrella experience and it is crucial to conduct more cross-cultural research to understand the obesity-personality relationship.
Another problem that could count as a weakness in current literature is that sociological measures are employed only by a limited number of studies. Since obesity is complex and cannot be thought of without one’s socio-economic environment, causal relationships between obesity and personality traits might be affected by it. Therefore, those studies that included demographic questionnaires and/or surveys should be followed.
Although studies do not offer a comprehensive treatment method for reducing weight that encompasses different personality types, they rather emphasize that certain personality types are more inclined to succeed at weight loss programs. It can be stated that weight loss programs should include personality assessment tests and behavioral therapy to offer the best possible therapy for people who seek to lose weight. Moreover, providing psychological support to those individuals in their journey of gaining healthier eating habits and losing weight could be considered as part of an integrated weight-management approach (Provencher et al., 2008). More longitudinal and clinical studies should be conducted to achieve more concrete clinical results with a narrowed focus on finding and developing successful intervention methods.
High conscientiousness may be an important factor for successful weight loss.
Conclusion
To conclude, most cross-sectional studies reach similar findings but when the time constant is factored in, as done in several longitudinal studies, results drastically change. The longitudinal results were only congruent with the associations with the agreeableness trait, finding an inverse association with agreeableness and becoming obese. On the other hand, cross-sectional results indicate associations between obesity and conscientiousness as well as neuroticism. However, not every cross-sectional study is limited to conscientiousness and neuroticism, as some studies show connections between obesity and all the Big-Five items. Therefore, current literature is suggesting further longitudinal and clinical studies to be conducted to better understand the associations between personality traits and obesity. Conscious dietary restraint is found to be related to some effort and self-control which not every obese patient might possess.¹⁰ Most papers suggest using personality assessment and making health interventions accordingly is useful in obesity management. To be specific, Magee et al., (2011) suggest that health messages should be specified to promote adherence for healthy behaviors for high neuroticism and low consciousness individuals (based on the cross-sectional data); while for high extraversion individuals, health messages should be specified to promote healthy behaviors in social settings (based on the longitudinal data).¹¹
References
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