Abstract
Objective
Personality influences lifestyle behaviors. Therefore, certain personality traits could contribute to obesity and the response to behaviorally based weight loss therapy.
Purpose
The aims of this study were to test the hypothesis that personality characteristics differ between lean and obese persons in the community, obese persons in the community and obese persons seeking weight loss therapy by enrolling in a comprehensive weight loss program, and in obese persons who were successful and unsuccessful in achieving behavioral therapy-induced weight loss.
Methods
The Temperament and Character Inventory was administered to 264 lean (body mass index (BMI) <25 kg/m2) and 56 obese (BMI≥35 kg/m2) subjects from the St Louis community and 183 obese patients (BMI = 44710 kg/m2) enrolled in the Washington University Weight Management Program (WUWMP), which involved weekly group behavioral therapy and diet education sessions for 22 weeks.
Results
Compared with lean subjects, obese subjects in the community scored higher in novelty seeking (19.7±5.9 vs 16.2±6.0, P<0.05), lower in Persistence (4.1±1.8 vs 4.8±1.7, P<0.05) and lower in self-directedness (32.1±7.6 vs 34.3±6.6, P<0.05.) Patients enrolled in the WUWMP scored higher than obese persons in the general population in both Reward Dependence (17.1±4.2 vs 15.7±4.3, P<0.05) and cooperativeness (36.9±5.4 vs 34.5±6.2, P<0.05). Patients who were successful in losing weight (>10% weight loss) after 22 weeks of behavioral therapy scored lower in novelty seeking than those who were unsuccessful in losing weight (<5% weight loss) (17.6±5.9 vs 20.2±5.9, P<0.05).
Discussion
These results suggest that personality traits differ between lean and obese persons, and between obese persons who enroll and who do not enroll in a comprehensive weight management program. Moreover, high scores in novelty seeking are associated with decreased success in achieving behavioral therapy-induced weight loss.
Keywords: personality, temperament, character, behavior modification
Introduction
Data from the most recent Nutrition and Health Examination Survey demonstrate that the prevalence of obesity remains a problem in both children and adults in the United States.1 Although approximately 45% of women and 30% of men are trying to lose weight,2 weight loss is difficult to achieve, and even those who lose weight often regain lost weight over time.3 Heritable personality traits can influence dietary intake4 and could be involved in the susceptibility to obesity and in the failure of obese persons to achieve successful weight loss. Several studies have evaluated the relationship between personality traits, assessed by the Karolinska Scales of Personality (KSP), and weight loss outcome in obese persons trying to lose weight.5–11 However, the results from these studies are inconsistent, possibly because of limitations in the KSP, which was designed to evaluate abnormal personality, rather than variations in normal personality.12,13
Recently, a new questionnaire, the Temperament and Character Inventory (TCI), was developed to provide a comprehensive evaluation of personality.14–16 The TCI measures seven dimensions of personality: (1) novelty seeking, (2) reward dependence, (3) harm avoidance, (4) persistence, (5) self-directedness, (6) self-transcendence and (7) cooperativeness. Each dimension has a unique genetic variance and is reproducible in clinical and general populations.14,16 By using the TCI, distinct personality characteristics were identified in patients who have eating disorders, such as bulimia, anorexia nervosa and binge eating disorder. For example, a high score in novelty seeking was associated with binging or overeating, whereas a low score was associated with a low appetite and decreased food consumption.17–22 Moreover, the TCI was able to identify specific components of personality that were associated with a rapid and sustained response to cognitive behavioral therapy for bulimia.23
The purpose of the present study was to use the TCI to (1) identify differences in personality characteristics between lean and obese persons, (2) determine whether personality characteristics in obese patients seeking weight loss therapy are different from those not seeking weight loss therapy and (3) determine whether specific components of personality are associated with successful behavioral therapy-induced weight loss.
Methods
Subjects
A total of 503 adults participated in this study. The subjects included a community sample of 264 lean (body mass index (BMI) 18.5–24.9 kg/m2) and 56 class II and III obese (BMI≥35 kg/m2) persons identified by random sampling from a standard telephone listing of residents in the St Louis greater metropolitan area, and a patient sample of 183 obese persons (BMI≥30 kg/m2) enrolled in the Washington University Weight Management Program (WUWMP) (Table 1). Subjects gave informed consent before participating in this study, which was approved by the Human Studies Committee of Washington University School of Medicine.
Table 1.
Characteristics of the study subjects
Community lean |
Community obese |
WUWMP obese |
|
---|---|---|---|
Total number | 264 | 56 | 183 |
Male | 95 | 23 | 41 |
Female | 169 | 33 | 142 |
Age (years) | 46.0±17.8 | 46.5±14.3 | 45.1±10.4 |
BMI (kg/m2) | 22.2±1.8 | 40.7±6.5 | 44.6±10.3 |
BMI 30.0–34.9 kg/m2 (no.) | 0 | 0 | 25 |
BMI >35.0 kg/m2 (no.) | 0 | 56 | 158 |
Abbreviations: BMI, body mass index; WUWMP, Washington University Weight Management Program.
Study protocol
The community sample of lean and obese subjects was obtained from a group of 629 men and women, living in the St Louis, Missouri metropolitan area, who participated in two surveys of personality, health and lifestyle. These surveys involved completing mailed questionnaires, 1 year apart.24,25 The second survey included the TCI, information on height and weight, and was used to provide the data for our study. Of these 629 subjects, 320 met the BMI inclusion criteria for the present study and were included as our community sample.
The patient sample consisted of obese persons who were actively involved in obesity treatment at the WUWMP. A total of 187 obese persons attended informational sessions between March 1998 and June 2000 to learn about the WUWMP; all persons completed the TCI questionnaire. Of these 187 attendees, 183 (98%) enrolled in the WUWMP. All 183 subjects completed at least 3 weeks of the 22-week program, and 131 (70%) completed the entire 22-week program. All subjects who completed at least 3 weeks of the program were included in an intention-to-treat analysis. The weight loss program involved weekly group behavior modification sessions, nutrition seminars, physical activity education and medical monitoring. Each subject was provided instructions for a 1000 kcal/day deficit diet, which included meal replacements consisting of shakes, snack bars and commercially prepared meal entrees. Height and weight was measured at the initial visit and body weight was recorded weekly.
Personality assessment
The TCI is a 240-question instrument, which measures four dimensions of temperament (novelty seeking, harm avoidance, reward dependence and persistence) and three dimensions of character (self-directedness, cooperativeness and self-transcendence) (Table 2).14,16 Temperaments are aspects of emotional responses and are stable through time, whereas characters are styles of mental self-government and may develop or mature through time. The test is written at a Flesch–Kincaid grade level = 3.4 (very easy). The questionnaire is composed of a series of true/false questions about the test taker’s likes and dislikes, emotional reactions, interests, attitudes, goals and values, which is then scored to assess the different dimensions of personality. Each of the seven dimensions is uniquely heritable and associated with specific neurotransmitter genes and regional brain activity.24 The internal consistency of the TCI measurements range from 0.76 to 0.89.14,16 The TCI scales are approximately normally distributed.14
Table 2.
Characteristics of personality dimensions assessed by the temperament and character inventory
Personality dimension |
High scorers | Low scorers |
---|---|---|
Temperament | ||
Harm avoidance | Worrying and pessimistic |
Relaxed and optimistic |
Fearful and doubtful | Bold and confident | |
Shy | Outgoing | |
Fatigable | Vigorous | |
Novelty seeking | Exploratory and curious | Indifferent |
Impulsive | Reflective | |
Extravagant and enthusiastic |
Frugal and detached | |
Disorderly | Orderly and regimented | |
Reward dependence |
Sentimental and warm | Practical and cold |
Dedicated and attached Dependent |
Withdrawn and detached Independent |
|
Persistence | Industrious and diligent | Inactive and indolent |
Hard-working | Gives up easily | |
Ambitious and overachiever |
Modest and underachiever | |
Perseverant and perfectionist |
Quitting and pragmatist | |
Character | ||
Self-directedness | Mature and strong | Immature and fragile |
Responsible and reliable | Blaming and unreliable | |
Purposeful | Purposeless | |
Resourceful and effective | Inert and ineffective | |
Self-accepted | Self-striving | |
Habits congruent with long-term goals |
Habits incongruent with long-term goals |
|
Cooperativeness | Socially tolerant | Socially intolerant |
Empathetic | Critical | |
Helpful | Unhelpful | |
Compassionate and constructive |
Revengeful and destructive | |
Ethical and principled | Opportunistic | |
Self-transcendence | Wise and patient | Impatient |
Creative and self-forgetful |
Unimaginative and self-conscious |
|
United with universe | Pride and lack of humility |
Statistical analysis
A Student’s t-test for independent samples was used to determine the statistical significance of differences between lean and obese subjects in the general population, obese subjects (BMI≥35 kg/m2) enrolled and not enrolled in a weight management program, and the TCI characteristics associated with successful (410% weight loss) and unsuccessful (<5% weight loss) weight loss. The criteria for successful and unsuccessful weight loss were defined by the amount of weight loss (i.e. ≥10% weight loss) that is associated with significant improvements in obesity-related medical complications and is the target goal for patients who enroll in our weight management program, and the amount of weight loss (i.e. <5% weight loss) that does not usually result in significant medical benefits. Data were analyzed by using SAS v6.12. A P-value p0.05 was considered to be statistically significant. F-tests were used to confirm that the homogeneity of variance assumption of the t-tests was met. All values are reported as mean±s.d.
Power calculations were performed for the three comparisons to detect a difference at the 0.05 level with a power of 80%. The critical effect size for comparing lean subjects and obese subjects in the general population was 0.17 of the s.d., for obese subjects in the general population and obese patients enrolled in the WUWMC was 0.22 of the s.d. and for patients enrolled in the WUWMC who were successful at weight loss and those who were not was 0.34 of the s.d.
Results
Lean and obese personality characteristics
In the general population, residing in the greater St Louis metropolitan area, obese subjects (BMI≥35.0 kg/m2) had significantly higher novelty seeking (effect size 0.58) and lower persistence and self-directedness scores than lean subjects (BMI <25.0 kg/m2) (Table 3). There was a trend toward decreased reward dependence and cooperativeness in obese than lean subjects, but the differences between groups was not statistically significant.
Table 3.
Personality characteristics in lean (BMI<25.0 kg/m2) and obese (BMI≥35.0kg/m2) persons in the general population
Personality dimension | Lean (n=264) | Obese (n=56) |
---|---|---|
Novelty seeking | 16.2±6.0 | 19.7±5.9* |
Harm avoidance | 13.3±7.3 | 14.7±7.5 |
Reward dependence | 16.8±4.0 | 15.7±4.3 |
Persistence | 4.8±1.7 | 4.1±1.8** |
Self-directedness | 34.3±6.6 | 32.1±7.6# |
Cooperativeness | 35.9±5.2 | 34.5±6.2 |
Self-transcendence | 15.3±6.3 | 15.2±6.3 |
Abbreviations: BMI, body mass index. Values significantly different from lean persons in the community value,
P<0.001,
P<0.005,
P = 0.02.
Obese enrolled and not enrolled in weight loss treatment
Obese subjects enrolled in treatment had significantly higher scores for reward dependence and cooperativeness than obese subjects in the general population (Table 4). Scores for novelty seeking, harm avoidance, self-directedness and self-transcendence were not significantly different between obese subjects enrolled and not enrolled in weight loss therapy. Persistence was not included in the final comparison between obese in the community and obese at the WUWMP, because the persistence scale in the TCI was modified after it was given to the subjects in the general populations. Therefore, a direct comparison cannot be made.
Table 4.
Personality characteristics in obese persons (BMI ≥35 kg/m2) in the community and obese persons (BMI ≥35 kg/m2) enrolled in the WUWMP
Personality
dimension |
Obese persons in
the community (n=56) |
Obese persons
enrolled in weight loss therapy (n=158) |
---|---|---|
Novelty seeking | 19.7±5.9 | 19.2±5.9 |
Harm avoidance | 14.7±7.5 | 15.9±8.5 |
Reward dependence | 15.7±4.3 | 17.1±4.2* |
Self-directedness | 32.0±7.5 | 31.0±8.7 |
Cooperativeness | 34.5±6.2 | 36.9±5.4** |
Self-transcendence | 14.5±6.2 | 16.1±6.1 |
Abbreviations: BMI, body mass index; WUWMP, Washington University Weight Management Program. Value significantly different than corresponding. Obese persons in the community value,
P<0.05,
P = 0.01.
Personality and weight loss outcome
Obese subjects who were successful in achieving ≥10% of their initial weight had lower scores for novelty seeking than obese subjects who lost <5% of their initial body weight after 22 weeks of weight loss therapy (Table 5). Scores for the other dimensions of personality were not significantly different between successful and unsuccessful subjects.
Table 5.
Personality scores in successful (≥10% weight loss) and unsuccessful (<5% weight loss) obese subjects enrolled in the WUWMP
Personality
dimension |
Unsuccessful
obese subjects (n=52) |
Successful
obese subjects (n=69) |
---|---|---|
Novelty seeking | 20.2±5.9 | 17.6±5.9* |
Harm avoidance | 16.3±8.4 | 15.7±8.4 |
Reward dependence | 17.3±4.0 | 16.7±4.4 |
Persistence | 5.1±1.8 | 5.5±2.0 |
Self-directedness | 30.3±9.7 | 32.1±8.6 |
Cooperativeness | 36.1±5.1 | 36.9±5.8 |
Self-transcendence | 15.2±6.2 | 16.9±5.7 |
Abbreviation: WUWMP, Washington University Weight Management Program. Value significantly different from corresponding unsuccessful obese subjects value,
P = 0.02.
Discussion
This study represents the first use of the TCI to evaluate personality characteristics in obese persons in the general population, and those enrolled in a comprehensive weight management program. The TCI has advantages over other measures of personality, because it provides a reproducible assessment of normal variations in personality. The major findings of the present study are that (1) obese persons have higher novelty seeking but lower persistence and self-directedness traits than lean persons in the general population, (2) obese persons enrolled in a comprehensive weight management program have higher reward dependence and cooperativeness than those in the general population and (3) obese persons who are successful at achieving initial weight loss have a lower novelty seeking trait than those who are not successful. These data suggest that specific personality characteristics are involved in the pathogenesis of obesity, and might help identify persons who are likely to respond to an obesity treatment program that includes comprehensive behavioral therapy.
We found that the score for novelty seeking temperament was higher in obese than lean subjects sampled from the general population. People who score high in novelty seeking tend to be thrill seekers, are easily bored, impulsive and try to avoid monotony. Therefore, these data suggest that overeating to avoid boredom might contribute to obesity. The results from our study are consistent with the results from previous studies, which found healthy dietary control and cognitive control of food intake are associated with lower scores in novelty seeking and obesity is associated with high reinforcement value associated with eating.7,22,26
Although data from some studies found that impulsiveness and monotony avoidance, assessed by the KSP scale, are higher in an obese population than a reference population,5,8 others have found that subjects who scored high in monotony avoidance were less likely to exhibit disinhibited eating behaviors in social situations,6 suggesting that environmental situations can influence the expression of personality characteristics.
Our community obese population also scored lower in self-directedness than lean persons. Self-directedness is a measure of internal organization, and the ability to set and pursue meaningful goals.16 Therefore, these data suggest that obese people may have a decreased ability to set weight loss goals and to maintain behaviors that lead to weight control. Conversely, patients with anorexia nervosa score high in persistence and have very strict and rigid patterns of food intake.17–21
Obese persons who sought treatment at our weight management program scored higher in reward dependence and cooperativeness than our sample of obese persons from the community. These personality characteristics are found in people who tend to be dedicated and sociable (high reward dependence score), tolerant, fair and supportive (high cooperativeness score). It is likely that our weight management program, which involves group behavior therapy and requires a considerable commitment from patients, attracted obese persons with these personality traits. Therefore, patients enrolled in our program, and presumably those who choose to enroll in other rigorous weight loss programs, represent a select subset of obese persons who are more likely to comply with treatment than other obese persons in the community. These results suggest that data reported from weight loss trials that are conducted in volunteers who chose to participate will generate more optimistic weight loss results than if therapy were initiated in the community.
Patients enrolled in our weight management program who were successful at losing weight had lower novelty seeking scores than those who did not achieve successful weight loss. These results imply that obese persons who may eat to combat boredom have considerable difficulty losing weight with standard behavior modification therapy. Similarly, data from previous studies have shown that obese people who scored high in the KSP scale of impulsivity lost less weight in a weight management program than those with lower scores,6 and that monotony avoidance was associated with difficulty in maintaining weight loss after jaw fixation.9,10 In contrast, Walker et al.11 found that only monotony avoidance was not associated with initial weight loss, and was only weakly associated with 12 month weight relapse. However, in that study, the initial weight management program was only 8 weeks long, and it is possible that treatment needs to be longer to see differences in weight loss between high and low scorers in novelty seeking.
The number of subjects who participated in this study was sufficiently large to detect even weak effects of personality on obesity, treatment seeking behavior and success in treatment (effect sizes between 0.17 and 0.34). The effects we observed were very strong and identified important differences in personality characteristics between groups. Specifically, novelty seeking personality trait was strongly associated with obesity in the general population (effect size 0.58), and reduced the likelihood of successful weight loss treatment outcome (effect size 0.44). These data suggest that high novelty seeking scores indicate a strong appetitive drive. Reward dependence was strongly associated with treatment seeking behavior, consistent with the notion that high reward dependence indicates a need for social approval. The effects of persistence and cooperativeness on the risk of being obese and seeking obesity treatment were moderate (effect sizes of 0.41–0.44).
In summary, the results of the present study demonstrate differences in selected personality characteristics between lean and obese persons, obese persons in the general population and those who enrolled in a rigorous weight loss program, and obese persons who are successful and those who are unsuccessful at losing weight with group behavior therapy. These data underscore the future potential usefulness of personality assessment in obesity management. Additional studies are needed to determine whether personality characteristics can be used to identify patients, in advance, who can benefit from behavioral weight loss therapy, whether personality characteristics change after weight loss in a program that includes behavior modification and finally, whether outcome can be improved by modifying therapy based on individual personality traits.
Acknowledgements
We thank Shane Cotter and the staff of the Washington University Weight Management Program for their assistance, and the study subjects for their participation.This study was supported by National Institutes of Health Grants MH60879 and DK 56341.
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