International Journal of Obesity (2003) 27, 1534–1540
& 2003 Nature Publishing Group All rights reserved 0307-0565/03 $25.00
www.nature.com/ijo
PAPER
Severe obesity and personality: a comparative
controlled study of personality traits
A Rydén*,1, M Sullivan1, JS Torgerson2, J Karlsson 1, A-K Lindroos2 and C Taft1
1
Health Care Research Unit, Institute of Internal Medicine, Sahlgrenska University Hospital, Göteborg University, Sweden;
Dept of Body Composition and Metabolism, Institute of Internal Medicine, Sahlgrenska University Hospital, Göteborg
University, Sweden
2
OBJECTIVE: The primary purpose was to assess personality trait differences between the severely obese seeking treatment and a
mainly non-obese reference group. We also investigated gender differences and differences between obese patients and obese
not seeking treatment.
METHOD: Personality traits were assessed using 7 of 15 scales from the Karolinska Scales of Personality (KSP): Somatic Anxiety,
Muscular Tension, Psychastenia, Psychic Anxiety, Monotony Avoidance, Impulsiveness, and Irritability. Patients from the
Swedish Obese Subjects (SOS) intervention study (n ¼ 3270, ages 37–57, 71% women) and the SOS reference study (n ¼ 1135,
54% women) completed the survey. Data presented in this study were gathered prior to treatment. Significance tests and effects
sizes were calculated.
RESULTS: Although statistically significant differences were found between obese patients and reference subjects on nearly all
personality traits, effect sizes were at most moderate. Of the three scales with moderate effects sizes, differences on Somatic
Anxiety and Psychastenia could be traced to items tapping condition-specific symptoms, e.g., problems with sweating and
breathing as indicators of Somatic Anxiety. Moderate differences on the Impulsiveness scale (men alone) could not be explained
by item composition. Further, the obese patients differed from obese in the reference group, and both obese and reference
women reported significantly higher levels on Somatic Anxiety, Muscular Tension and Psychic Anxiety compared to men (effect
size: small).
CONCLUSIONS: Our results provided no evidence of a general obese personality profile, instead considerable heterogeneity in
personality traits was observed across our obese samples (treatment seekers vs non-seekers, men vs women) and generally only
small differences were noted compared to a reference study population. Further research is needed to investigate if the
somewhat elevated levels of Impulsiveness, particularly among male obese patients, is affected by weight loss. When assessing
personality traits in diseased groups consideration should be given to possible confounding from, e.g., somatic symptoms.
International Journal of Obesity (2003) 27, 1534–1540. doi:10.1038/sj.ijo.0802460
Keywords: obesity;personality;patients;reference subjects;gender differences
Introduction
Personality traits can be defined as stable, fundamental
dimensions of personality, influencing our thoughts and
behaviours in a variety of situations. 1 According to this
definition personality may, at least partly, be related to
lifestyle and eating behaviour, and therefore also to obesity.
*Correspondence: Dr A Rydén, Health Care Research Unit, Institute for
Internal Medicine, Sahlgrenska University Hospital, SE-413 45 Göteborg,
Sweden. E-mail: [email protected]
Grants: The Swedish Council for Working Life and Social Research
(project 2001–1106), the Swedish Foundation for Health Care Sciences
and Allergy Research (project V96 065), the Swedish Research Council
(project Y0748), the Faculty of Medicine, Göteborg University.
Many authors agree that obesity is not a unitary syndrome,
either from a physiological, psychological, or psychiatric
viewpoint.2 This may explain why results concerning the
relationship between obesity, personality traits, and psychopathology have been divergent. Also, conceptual and
measurement models have differed over time. Some authors
have concluded that obese do not differ from a general
population on nonweight-related personality traits.3–5 However, Larsen and Torgersen6 noted higher scores on oral
cluster traits for the obese and, using the Karolinska Scales of
Personality, Björvell et al7 found that an ‘impulsiveness
syndrome’ characterised the obese. According to a study
by Palme and Palme,8 using the same instrument, obese
women were more anti-social and anxiety prone compared
to a population average. A recent study by Fassino et al 9
Personality traits among obese
A Rydén et al
1535
compared obese and non-obese women and, according to
their results, the obese women’s temperament and character
were more irascible, impulsive, passive, insecure, nervous,
and frail.
Studies on personality within the obese group indicate a
large variability where, for example, differences have been
noted among patients due to undergo the same treatment
(surgery).10–12 Differences have also been noted between
patients choosing different treatment (an in-hospital combined behavioural program or jaw-fixation), where those
who preferred behavioural treatment were more psychastenic, while patients choosing jaw-fixation scored higher on
Monotony Avoidance.7
Few personality studies on obese samples have analysed
gender differences, despite research indicating that BMI
affects psychological functioning in men and women
differently2,13 This is partly due to the fact that most obese
patient samples consist predominantly or exclusively of
females. However, in a population-based study, Faith et al
found that increasing BMI for women was associated with
increased neuroticism and reduced extraversion, whereas for
men it was associated with increased extraversion and
psychoticism.14 It should be noted, though, that all associations were weak.
The primary aim of this study was to further assess if
severely obese men and women seeking treatment differed
from a reference group regarding personality traits. We also
wanted to investigate gender differences and differences
between obese patients and obese not seeking treatment.
Methods
In the present study we have used data from two ongoing
Swedish studies, the Swedish Obese Subjects (SOS) study15–17
and the SOS reference study. 18
SOS study
The SOS study is a nation-wide controlled, prospective trial
that started 1987. The SOS project is divided into two parts, a
cross-sectional registry study and a prospective intervention
study (inclusion of patients into both studies was completed
in January 2001). The registry study includes more than 6000
obese participants. From this pool, 2010 surgical candidates
and their conventionally treated controls (n ¼ 2037) were
recruited to the subsequent intervention study. Surgical cases
(treated with gastric banding, vertical banded gastroplasty or
gastric by-pass) undergo operations and follow-up examinations at 25 county or university hospitals in Sweden. The
conventionally treated, non-surgical cases (treated according
to local routines) are followed at 480 primary health care
centres from 18 of the 24 counties. All of these patients will
be followed on a regular basis for 20 years. The SOS study is
not randomised due to ethical committee reasons.17 In order
to avoid any systematic difference between the two groups
prior to treatment, a computerised matching procedure
selects the optimal control case to match each included
surgical patient. The selection is based on an algorithm
moving the mean values of the matching variables of the
control group toward the current mean values of the
surgically treated patients. In this way, a group match rather
than an individual match is undertaken. The procedure takes
into account 18 variables, of which six are psychosocial. The
intervention trial is designed to test if the negative effects of
severe obesity on mortality, morbidity, and quality of life are
reduced by weight reduction in the long term. Inclusion
criteria are age (37–57 years) and BMI (Z34 kg/m2 for men
and Z38 kg/m2 for women). All subjects undergo an
extensive health examination at study start and complete a
battery of questionnaires (on for example, socio-demographics, psychological variables, eating behaviour) at
regular intervals. More detailed descriptions of the SOS study
design, recruitment and assessment procedures have been
reported previously.15–17 The ethical committees of all
medical faculties in Sweden approved the study and
informed consent was obtained from all patients.
SOS reference study
In order to obtain comparable reference material on mainly
non-obese subjects a population study has been performed.
Women and men, aged 37–60, living in two typical suburban
areas in Sweden were randomly selected. All together 2037
subjects were invited and 1135 (54% women) agreed
to participate (55.7% response rate). All participants
were health examined between 1994 and 1999, and
completed the same questionnaires as in the SOS Registry
study. Follow-up examinations are planned after 10, 15
and 20 years. The ethical committees approved the SOS
reference study and informed consent was obtained from all
participants.
Participants
The present study is based on data from 3270 SOS intervention patients and on the 1135 SOS reference individuals.
Data from 777 patients are missing since questions related to
five of the seven KSP factors were not initially included. The
patient sample therefore consists of 1626 receiving surgical
and 1644 receiving conventional treatment. Despite the
lower BMI inclusion cut-off value for male patients, females
were over-represented in this group (71%). Demographic and
social background characteristics are presented in Table 1. In
comparison to the reference group the obese had lower
levels of education and more reference men were married/
cohabiting.
Anthropometric measures
Body weight was measured to the nearest 0.1 kg. using
calibrated balances or electronic scales. Height was measured
International Journal of Obesity
Personality traits among obese
A Rydén et al
1536
to the nearest 0.01 m. BMI was calculated by dividing body
weight by height squared (kg/m2).
ing for energy consumption. The Psychic Anxiety scale (10
items) reflects social anxiety, insecurity, and worrying.
Extraversion-related. Monotony Avoidance (10 items) is a
sensation-seeking scale, concerning a need for novelty and
change, preference for strong stimuli and an adventurous
life-style. The Impulsiveness scale (10 items) is assumed to
reflect tendencies to act on the spur of the moment, lack of
planning and rapid decision-making.
The Karolinska Scales of Personality (KSP)
The KSP was constructed to cover specific areas of importance for research in healthy subjects, but also to identify
dimensions of vulnerability to various personality and
psychiatric disorders.19.In contrast to many other personality
inventories it was never intended to cover ‘the whole
personality’ or reveal certain psychopathological profiles.
The KSP originally consists of 15 scales (135 items) grouped
into three main domains: anxiety proneness, extraversionrelated and aggression.20 However, due to the extensive
battery of mailed questionnaires in the SOS study only seven
of these scales (75 items) were selected to match our research
questions.
Aggression. The Irritability scale (5 items) concerns a readiness to explode with negative affect at the slightest
provocation and feelings of irritation.
The respondents rated each item on a 4-step response scale
ranging from ‘does not apply at all’ to ‘applies completely’.
Scores were summed giving a score between 10 and 40 for
each scale, excepting Irritability where the score ranges
between 5 and 20. Item examples for each scale are presented
in Appendix A.
Anxiety proneness. Somatic Anxiety (10 items) reflects
autonomic disturbances, diffuse distress, and panic attacks.
Muscular Tension (10 items) concerns subjective tenseness
and aches, and difficulties in relaxing. Psychastenia (10
items) is a scale reflecting cognitive anxiety, implying a
scanty supply of mental energy and difficulty in compensat-
Statistical methods
Descriptive statistics with 95% confidence interval (C.I.)
were calculated according to standard procedures. Differences between groups were tested with the Mann-Whitney U
test. Due to the large number of statistical comparisons
Bonferroni correction was applied within each set of
responses in order to guard against inflated Type I errors.
Thus, the p level was set at 0.004 (0.05/14). The magnitude of
group differences was further determined by calculating
effects sizes (ES) using Cohen’s d (M1M2/spooled where
spooled ¼ O[(s21 þ s22)/2]).21 ES makes it possible to judge the
importance of a group difference and was judged against
standard criteria proposed by Cohen: trivial (o0.20), small
(0.20o0.50), moderate (0.50o0.80) and large (Z0.80).
Table 1 Comparison of the SOS patients with the SOS reference study
population
Obese patients
Characteristic
Age
Height (m)
Weight (kg)
BMI (kg/m2)
Marital status (%)
Married/cohabiting
Single/divorced/widowed
Education level (%)
Compulsory
Upper secondary
University
Table 2
Reference group
Men
n ¼ 912
Women
n ¼ 2358
Men
n ¼ 524
Women
n ¼ 611
48.1
1.80
128.9
39.9
48.0
1.65
113.4
41.8
49.8
1.79
83.3
25.8
49.3
1.66
68.0
24.7
74.9
25.1
77.4
22.6
82.0
18.0
77.6
22.4
40.4
45.8
13.8
36.7
43.8
19.5
24.7
46.0
29.3
25.6
38.0
36.4
Results
Obese patients vs references subjects
Scores from the KSP personality scales for obese and
reference subjects are presented in Table 2 and ES in Figure 1.
Mean scores (95% C.I.) of the Karolinska Scales of Personality in obese patients and reference study population
Obese men
(n ¼ 912)
KSP scale
Anxiety
SA
MT
Psy
PA
18.56
17.39
23.36
18.69
Extraversion
MA
Imp
Aggression
Irr
(18.17–18.95)
(17.02–17.76)
(23.02–23.69)
(18.32–19.07)
Reference men
(n ¼ 522)
Obese women
(n ¼ 2358)
(14.71–15.50)
(14.92–15.75)
(20.19–20.92)
(17.69–18.56)
0.000
0.000
0.000
0.218
20.40
20.06
23.52
21.68
23.44 (23.13–23.75)
24.42 (24.15–24.69)
24.01 (23.63–24.38)
21.91 (21.56–22.26)
0.048
0.000
10.76 (10.58–10.94)
10.03 (9.84–10.22)
0.000
Min–max score ¼ 10–40, except Irritability 5–20.
International Journal of Obesity
15.11
15.33
20.56
18.12
P%
%
(20.14–20.65)
(19.81–20.32)
(23.31–23.73)
(21.42–21.95)
Reference women
(n ¼ 611)
(16.51–17.31)
(16.82–17.71)
(20.67–21.37)
(19.90–20.74)
0.000
0.000
0.000
0.000
22.43 (22.22–22.63)
24.06 (23.87–24.23)
23.35 (22.99–23.70)
22.27 (21.94–22.60)
0.000
0.000
10.78 (10.67–10.89)
10.17 (9.98–10.35)
0.000
Significant at P ¼ 0.004 (0.05/14), Mann–Whitney U test.
16.91
17.26
21.02
20.32
P%
Personality traits among obese
A Rydén et al
1537
Figure 2 Differences (effects sizes) in personality scales between obese
Figure 1 Differences (effect sizes) in personality scales between obese
patients and obese in the reference study population.
patients and the reference study population by gender. *NB. MA negative
sign.
Anxiety proneness. Diversity was noted concerning the
anxiety scales. Both obese men and women displayed more
Somatic Anxiety (ES ¼ moderate), Muscular Tension (ES ¼
small) and Psychastenia (ES ¼ moderate) than their reference
counterparts. Three of 10 items in Somatic Anxiety explained most of the difference: ‘often feel uncomfortable and
ill at ease for no obvious reason’, ‘can suddenly start
sweating without obvious reason’ and ‘sometimes feel I
don’t get enough air to breathe’. Two of 10 Muscular Tension
items differed more than the others: ‘often have aches in
shoulders and in the back of my neck’ and ‘body often feels
stiff and tense’. The largest differences in Psychastenia were
found on 2 of the 10 items and these concerned lack of
energy: ‘to get something done I have to spend more energy
than others’ and ‘get fatigued more easily than most ‘.
Obese women reported significantly more Psychic Anxiety
than reference women (ES ¼ small), while no differences
were found between obese and reference men. Three items
concerning self-confidence contributed most to the differences between obese and reference women: ‘don’t feel at ease
when meeting people I don’t know too well’, ‘don’t have
much self-confidence’ and ‘am quite self-conscious in most
social situations’.
Extraversion-related scales. Diversity was also noted concerning the extraversion-related scales. Obese women reported significantly less Monotony Avoidance then reference
women (ES ¼ trivial), but no significant difference was found
for men. However, more Impulsiveness was reported by both
obese women (ES ¼ small) and men (ES ¼ moderate), with
item differences quite evenly distributed over all items.
Aggression. Finally, both female and male obese subjects
displayed more Irritability (ES ¼ small) and two of 5 items
explained most of the difference: ‘people sometimes bother
me by just being around’ and ‘am almost always patient with
others’ (reversed item).
Obese in the reference group vs patients
To illustrate possible differences between obese not seeking
treatment and obese patients, we sub-sampled persons in the
reference group with a BMI Z30 (n ¼ 115, 46% men, BMI
33.1). Compared to the non-obese this group did not differ
on any personality scale. When compared to the obese
patients the non-patients scored significantly lower on all
personality scales, except Irritability (p 0.029) and Monotony
Avoidance (p 0.816). Effect sizes are shown in Figure 2 and
the pattern of differences were similar to that between
patients and the total reference group (see Figure 1). Due to
the small sample no gender analyses were performed.
Women vs men
As can be seen in Table 3, both obese and reference women
scored significantly higher than men on all anxiety scales
International Journal of Obesity
Personality traits among obese
A Rydén et al
1538
Table 3
Mean score differences between women and men within the obese patient group and the reference study population, respectively
Obese patients
KSP scale
Anxiety
SA
MT
Psy
PA
Extraversion
MA
Imp
Aggression
Irr
Difference women–men
P*
Reference subjects
ESa
Difference women–men
P*
ESa
1.84
2.67
0.16
2.99
0.000
0.000
0.392
0.000
0.30
0.44
0.03
0.49
1.80
1.93
0.46
2.17
0.000
0.000
0.184
0.000
0.37
0.37
0.11
0.42
1.01
0.37
0.000
0.020
0.21
0.09
0.66
0.37
0.017
0.112
0.15
0.09
0.02
0.868
0.00
0.14
0.478
0.06
*
Significant at P ¼ 0.004 (0.05/14), Mann–Whitney U test.
Cohen’s d; trivial o0.20, small 0.20o0.50, moderate 0.50o0.80, large Z0.80.
a
except Psychastenia. For both groups of women these
differences were small according to ES cut-offs. When
looking at item level the differences were quite evenly
distributed on all anxiety scales. A statistical difference was
also noted between women and men in the obese group
regarding Monotony Avoidance, with men scoring higher
(ES ¼ small).
Discussion
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 lifestyle 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.6
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.
International Journal of Obesity
Our results showing higher levels of Somatic Anxiety,
Muscular Tension, and Psychastenia are in line with previous
studies7,8,22 that also included obese persons seeking treatment. We know very little about why obese persons seek
treatment through participation in studies. Are they primarily motivated by the psychological burden of this condition
or the physical problems it frequently entails? In general
severely obese tend to suffer from co-morbid conditions.23,24
This is also the case with the SOS patients who, for example,
have a higher prevalence of diabetes, high-risk levels of
triglycerides and HDL, hypertension and joint problems.
Since Somatic Anxiety and Muscular Tension tap somatic
concerns, the elevated levels on these traits among persons
seeking medical attention is then perhaps not surprising.
Also, items that mainly contributed to the differences in our
study reflect condition specific problems, such as problems
with sweating, breathing, fatigue, body tension, and pain. It
has been demonstrated that weight reduction improves
functional health, for example, surgically induced weight
loss is associated with a marked relief in dyspnea and chest
pain.25,26 However, symptoms like these could also be
interpreted as reactions to underlying mental stress, predisposing a life-style causing obesity, and consequently amplify
the condition specific problems.
Among other things, the Psychastenia scale is supposed to
measure mental energy. Unfortunately, items comprising
this scale are phrased in such a way that they can be
interpreted in different ways depending on context and/or
subject. Items like ‘to get something done I have to spend
more energy than most’ and ‘I get fatigued more easily than
most’ may just as well reflect physical as mental energy. This
ambiguity makes interpretation of the results difficult. Since
obese people generally have a physically more inactive
lifestyle and thus tend to be less fit, the difference in
Psychastenia could partly be explained by somatic factors.
On the other hand, Psychastenia could be a personality trait
facilitating obesity and, in turn, elevated levels of Somatic
Anxiety and Muscular Tension.
Personality traits among obese
A Rydén et al
1539
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 selfesteem. Being obese is a more stigmatised condition for
women,2,13,27 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 al9 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 distressed16 and it has
been proposed that all forms of negative affect contribute to
increased aggression.28 Distress has also been linked to a
breakdown of impulse control.29 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.3,30 Differences have also been noted between
patients who prefer more drastic weight-reduction methods,
such as surgery31,32 or appetite depressants33 compared to
patients who prefer conventional treatment.
Regarding gender differences, females in both groups were
slightly more anxiety prone than their male counterparts.
This is an often-reported common phenomenon in Western
countries, see Feingold’s meta-analysis.34 Why gender differences like these are more pronounced in modern cultures is
debated. Costa et al35 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.
Since the SOS patients have been obese for more than 20
years on average, we are aware that the personality trait
scores in this study may reflect reactions to the condition as
well as an underlying predisposition. It is also possible that
some traits relate to causes, while others are a result of the
condition. However, in the clinical setting personality data
could provide a context for understanding the patient,
interpreting problems and selecting type of treatment. Also,
traits like anxiety, impulsiveness, and aggression are implicated in subclinical stress reactions and may be mediated
by coping strategies. Personality and coping could therefore
have important bearing on the hypothesis that an inability
to handle stress might be one factor leading to hypersensitivity in the HPA axis, setting off neuroendocrine and
metabolic disturbances.36–38 Such disturbances may result
in greater central fat accumulation that in turn is an
important risk factor for cardiovascular disease and diabetes
type 2. This is a topic for future research.
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Appendix A. Abbreviated items from each
personality factor
Anxiety proneness
Somatic anxiety
Sometimes when upset, I suddenly feel as if my legs are too
weak to carry me.
Sometimes my cheeks burn even if it isn’t particularly hot.
Muscular tension
I often find myself gnashing my jaws together for no real
reason.
I have difficulty sitting in a relaxed position even in a
comfortable chair.
Psychastenia
I don’t mind being interrupted when I’m working with
something. (-)
I easily feel pressure when I’m urged to speed up.
Psychic Anxiety
I often worry about things that other people look upon as
trifles.
Even though I know I’m right, I often have great difficulty
getting my point across.
Extraversion-related
Monotony Avoidance
I prefer people who come up with exciting and unexpected
activities.
To be on the move, travelling, change and excitement –
that’s the kind of life I like.
Impulsiveness
I have a tendency to act on the spur of the moment
without really thinking ahead.
I often throw myself into things too hastily.
Aggression
Irritability
Sometimes people bother me by just being around.
I can’t help being a little rude to people I don’t like.