Association between weight perception and psychological distress

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Nov 27, 2007 - 1Exercise, Health and Performance Faculty Research Group, Faculty of Health Sciences, The University of Sydney, Sydney,. New South Wales ...
International Journal of Obesity (2008) 32, 715–721 & 2008 Nature Publishing Group All rights reserved 0307-0565/08 $30.00 www.nature.com/ijo

ORIGINAL ARTICLE Association between weight perception and psychological distress E Atlantis1 and K Ball2 1 Exercise, Health and Performance Faculty Research Group, Faculty of Health Sciences, The University of Sydney, Sydney, New South Wales, Australia and 2Centre for Physical Activity and Nutrition (C-PAN), School of Exercise and Nutrition Sciences, Deakin University, Deakin, Victoria, Australia

Background: Obesity is a well-known cause of cardiovascular disease burden and premature death, but effects on depressive symptoms remain equivocal. Depressive symptoms may be more common among the obese individuals who perceive themselves as overweight, rather than those who perceive themselves as having an acceptable weight. Our aim was to determine whether weight status and weight perceptions are independently associated with psychological distress. Methods: We conducted a cross-sectional study using data from the Australian National Health Survey 2004–2005 (N ¼ 17 253). All variables were collected by self-report. Adjusted multinomial logistic regression analysis was conducted to generate prevalence odds ratios with 95% confidence intervals (95% CI) for medium (Kessler Psychological Distress Scale (K10) scores of 20–29) and high (K10 scores of 30–50) psychological distress (compared with K10 scores of 10–19 as the reference) associated with weight status (standard body mass index (BMI) cutoffs for underweight, overweight and obesity vs normal weight), weight perception (perceived underweight and overweight vs acceptable weight) and weight misperception (incorrect with BMI vs correct with BMI) adjusting for numerous important covariates. Results: Overweight and underweight perception increased the odds of medium (40 and 50%) and high (50 and 120%) psychological distress, whereas weight status and weight misperception were not associated with psychological distress in adjusted analysis. Gender, alcohol consumed per week and post-school education were not significant covariates (at Po0.10 level). Conclusions: Overweight and underweight perception rather than weight status or weight misperception are significant risk factors associated with medium and high psychological distress prevalence and effects appear to be uniform for men and women. Well-designed prospective studies are still needed to determine whether weight perceptions cause psychological distress, and if so, whether symptoms are significantly reduced following effective intervention. International Journal of Obesity (2008) 32, 715–721; doi:10.1038/sj.ijo.0803762; published online 27 November 2007 Keywords: weight perception; misperception; underweight; overweight; depression; mental health

Introduction Obesity is a well-known cause of cardiovascular disease burden and premature death,1–3 but effects on depressive symptoms remain equivocal due to an absence of good quality evidence. Major depression is one of the most prevalent psychiatric disorders in developed populations,4,5 and studies investigating the etiological effects of obesity on

Correspondence: Dr E Atlantis, Exercise, Health and Performance Faculty Research Group, Faculty of Health Sciences, The University of Sydney, 75 East Street, LIDCOMBE, Sydney, New South Wales 2141, Australia. E-mail: [email protected] Received 9 June 2007; revised 25 September 2007; accepted 30 September 2007; published online 27 November 2007

depressive symptoms account for the vast body of published literature relating to obesity and psychological morbidity. The etiological body of evidence consists mostly of crosssectional studies,4,6–14 and relatively fewer prospective cohort studies,15–18 and is riddled with inconsistencies. Obesity has conferred significant associations with depressive symptoms for adults,4,7,16,18 for men but not women,15 for women but not men6,9,10 and for severe obesity only,12 whereas other studies found no association11,13,14,17 or negative association.8 Of the few intervention studies that have investigated weight-loss effects on depressive symptoms in obese patients, none were randomized controlled trials.19–24 One of these experimental studies reported a reduction in depressive symptoms at 4-year follow-up,20 but effects disappeared at 10-year follow-up.21 Inconsistent findings may be partly due to methodological heterogeneity

Weight perception and psychological distress E Atlantis and K Ball

716 between studies. For example, covariates used for adjustment in statistical models varied immensely, and no study was simultaneously controlled for most of the known confounding factors such as age, gender and other sociodemographic characteristics, physical health, smoking and physical activity. Another possibility is that weight perception rather than the weight status per se is causally related to depressive symptoms. Obese individuals across the age spectrum experience weight-related stigma.25–28 Such stigma could plausibly lead to the feelings of distress and depression. It is also well documented that substantial proportions of normal-weight boys and girls29,30 as well as men and women31–33 misclassify themselves as being overweight, and, conversely, that many overweight individuals mistakenly classify themselves as being within a healthy weight range.29,31,32 Such weight misperceptions may in fact explain why pervasive inconsistencies exist in the obesity-depression literature. Specifically, depressive symptoms may be more common among the subgroup of obese adults who perceive themselves as overweight, rather than obese individuals who perceive themselves as having an acceptable weight. Few studies have investigated this hypothesis. Two studies in Chinese adolescents found higher depressive symptoms associated with overweight perception compared with normal or not overweight perception.29,30 Another study in Dutch adolescents found stronger associations between overweight perception and anxious/depressive symptoms compared with actual overweight status.34 Whether weight perceptions and weight status are independently associated with depressive symptoms is not yet known. Thus, the aim of the present study was to investigate whether weight status and weight perceptions are independently associated with nonspecific psychological distress in a nationally representative sample of adults, adjusting for several important covariates. This type of study permits delineating potential effects of weight status and weight perceptions on psychological distress and could identify a unique subgroup of individuals at increased risk of psychological morbidity.

more person aged 18 years or above. The NHS 2004–2005 response rate of 89% (19 501/21 808) was calculated by dividing the number of private dwelling units with fully completed interviews by the total number of sampled private dwelling units.35 There were data for 25 906 cases, of which 73% (19 018/25 906) were for adults aged 20 years or above. Data for psychological distress were missing for 0.1% (8/19 018) and data for body mass index (BMI) could not be derived for 9% (1747/19 018) of this sample, due to missing height and/or weight values. Complete data were available for the remaining 17 253 adults (8122 men, 9131 women) for analysis in this study.

Dependent variable Psychological distress. Psychological distress was determined from data obtained using the Kessler Psychological Distress Scale (K10).36.In the Australian National Survey of Mental Health and Well-Being, the K10 was found to accurately discriminate cases from noncases (area under the curve of 0.90 using receiver operating characteristic curve analysis) of any current DSM-IV anxiety or mood disorder diagnosed using the World Health Organization’s Composite International Diagnostic Interview with face-to-face interviews by trained lay interviewers.37 In the K10, respondents are asked to rate how often, in the past 4 weeks, they felt negative emotions on 10 scales. Response options for each scale include (1) all of the time, (2) most of the time, (3) some of the time, (4) a little of the time and (5) none of the time. Scores for each scale are equal to the reverse of the ordinal value, so response option 1 ¼ all of the time is assigned a score of five, whereas response option (5) none of the time is assigned a score of 1. Scores for the 10 scales are summed and can range from 10 to 50. The Cronbach’s a coefficient for the K10 in this sample was 0.855 (coefficients for each scale were between 0.833 and 0.854). Cutoffs used to define low (scores 10–15), medium (scores 20–29) and high (scores 30–50) psychological distress categories were chosen based on the Australian normative comparative data for stratum-specific likelihood ratios for correctly discriminating cases from noncases,37 and for mental health service utilization.38

Methods Sample We conducted secondary analyses of cross-sectional data from the Australian National Health Survey (NHS) 2004– 2005; the most recent of a series of nationally representative surveys conducted by the Australian Bureau of Statistics. Information about health status, use of health services, health-related lifestyle factors, demographic and socioeconomic characteristics of participants were obtained from residents of sampled private dwellings by trained interviewers. Private dwellings defined as homes, flats/units, caravans, tents and other structures being used as private places of residence were included when containing one or International Journal of Obesity

Risk factor variables Body mass index. Body mass index was derived from selfreport, height and weight values and computed as weight in kilograms divided by height in meters squared. Standard (internationally used) BMI cutoffs were used to define underweight (o18.5 kg m2), acceptable (also termed healthy) weight (18.5–24.9 kg m2), overweight (25.0– 29.9 kg m2) and obesity (X30.0 kg m2) categories. Weight perception. Self-perceived weight status was determined by asking participants ‘do you consider yourself to be acceptable weight, underweight or overweight?’ This single question item was the same or very similar to what was

Weight perception and psychological distress E Atlantis and K Ball

717 previously used to determine weight perceptions in population surveys conducted both here in Australia,33 and in the US.31 Misperception. Independent effects of weight misperception were examined, as we further hypothesized possible associations with psychological distress independent of weight perception and weight status. Misperception was determined as incorrect weight perception according to actual BMI weight status and described as incorrect with BMI, compared with correct with BMI.

Covariate variables The following covariates were included because of their potential association with psychological distress: gender (male, female); age (20–39, 40–59, 60 years or above); leisure-time physical activity (duration multiplied by intensity weighted, 3.5 for walking, 5.0 for moderate and 7.5 for vigorous intensity of leisure-time physical activity during the past 2 weeks was used to categorize respondents into sedentary (o100 including no exercise), low (100 to o1 600)); moderate-to-high (X1 600), smoking status (current smoker, ex-regular smoker, never smoked); alcohol (weekly intake: percentile cutoffs were used to generate three equal groups); medication used for mental well-being (includes prescribed medicine, herbal/natural medicine and vitamin/ mineral supplements used in the past 2 weeks to ‘improve concentration or reduce stress’); number (sum (0–1, 2–3 and X4) of current medical conditions (told by a doctor or nurse), which had lasted or were expected to last 6 months or more); marital status (married or defacto relationship, not married or defacto relationship); income (gross weekly in AUD: not applicable or not reported, o$200, $200-$354, $355-$632, X$632); main language spoken at home (English only, other); country of birth (Australia, main other Englishspeaking countries, other non-English-speaking countries); employment status (unemployed looking for work, employed part-time, employed full-time, not in the labor force) and post-school education/qualification (none or level not determined, has post-school education/qualification).

Statistical analyses Statistical analyses were performed using SPSS 15.0 (SPSS Inc., Chicago, IL). Unadjusted multinomial logistic regression analysis was conducted to generate prevalence odds ratios with 95% confidence intervals (95% CI) for medium (K10 scores of 20–29) and high (K10 scores of 30–50) psychological distress (compared with K10 scores of 10–19 as the referent category) associated with weight status, weight perception and weight misperception. Adjusted multinomial logistic regression analysis was conducted first to examine independent effects of weight status, weight perception and weight misperception on psychological distress and secondly to examine these associations with

adjustment for covariates and gender interactions (BMI*gender, weight perception*gender, weight misperception*gender). Gender interactions were initially examined because of conflicting findings for obesity effects on psychological distress among men and women in the published literature,6,9,10,15 but subsequently removed because reliable interaction effects could not be determined due to insufficient or missing data in several stratums.

Results Table 1 presents sample size and distribution of adults stratified by weight status, weight perception and psychological distress. The overall prevalence of medium and high psychological distress was 14.3% (12.3% for men; 16.2% for women) and 3.8% (3.1% for men; 4.5% for women), respectively. Table 2 presents prevalence odds ratios for psychological distress associated with weight status, weight perception and weight misperception as unadjusted, adjusted for each other risk factor alone and secondly, with all covariates. All covariates, other than gender in adjusted analysis for medium or high psychological distress, and alcohol weekly consumption and post-school education in adjusted analysis for medium psychological distress, were statistically significant (at Po0.10 level). For weight status, obesity (BMI X30.0 kg m2) and underweight (BMI o18.5 kg m2) increased the odds of medium (40 and 60%) and high (60 and 240%) psychological distress in unadjusted analysis, but effects were no longer significant after adjustment for weight perception, misperception and all covariates. For misperception, incorrect weight perception decreased the odds of medium (10%) psychological distress in unadjusted analysis, but not after adjustment for weight status, weight perception and all covariates. In contrast, overweight and underweight perception increased the odds of medium (50 and 120%) and high (70 and 360%) psychological distress in unadjusted analysis and effects remained highly significant after adjustment for other risk factors and all covariates. In adjusted analysis, overweight and underweight perception increased the odds of medium (40 and 50%) and of high (50% and 120%) psychological distress, whereas weight status and weight misperception were not associated with psychological distress. Results show that overweight and underweight perception rather than weight status or weight misperception were significant risk factors associated with medium and high psychological distress prevalence, and effects appeared to be uniform for men and women.

Discussion Our initial finding that obesity significantly increased the odds of psychological distress when examined in isolation is International Journal of Obesity

Weight perception and psychological distress E Atlantis and K Ball

718 Table 1 Sample size and distribution of adults stratified by weight status, weight perception and psychological distress, from the Australian National Health Survey 2004–2005 Weight perception

Psychological distress

Weight status BMI 18.5–24.9

BMIo18.5

BMI 25.0–29.9

BMIX30.0

Total

Acceptable weight

Low Medium High

4249 2003 178

138 67 10

2305 958 101

311 150 16

7003 3178 305

Underweight

Low Medium High

233 187 47

90 81 30

27 20 1

10 4 0

360 292 78

Overweight

Low Medium High

322 218 27

2 3 2

1611 957 105

1632 1012 146

3567 2190 280

7464

423

6085

3281

17 253

Total

36

Psychological distress determined using scores from the Kessler Psychological Distress Scale ; low ¼ 10–19, medium ¼ 20–29, high 3–50; BMI ¼ body mass index (units in kg m2, computed as weight in kilograms divided by height in meters squared).

Table 2 Prevalence odds ratios (95% confidence intervals) for medium and high psychological distress associated with weight status (BMI category), weight perception and weight misperception for adults from the Australian National Health Survey 2004–2005, N ¼ 17 253 Prevalence of medium psychological distress (%)

Unadjusted

P-value

Adjusteda

Weight status BMI 18.5–24.9 BMI o18.5 BMI 25.0–29.9 BMI X30.0

13.7 19.1 13.1 17.5

1 1.6 (1.3, 2.1) 0.9 (0.9, 1.0) 1.4 (1.2, 1.5)

o0.001 0.31 o0.001

1 1.3 (1.0, 1.7) 0.8 (0.7, 0.9) 1.0 (0.9, 1.2)

Weight perception Acceptable weight Underweight Overweight

12.3 21.4 17.0

1 2.2 (1.8, 2.6) 1.5 (1.4, 1.6)

o0.001 o0.001

Misperception Correct with BMI Incorrect with BMI

14.8 13.3

1 0.9 (0.8, 1.0)

3.4 9.9 3.4 4.9

Weight perception Acceptable weight Underweight Overweight Misperception Correct with BMI Incorrect with BMI

Risk factor

Adjustedb

P-value

0.09 0.004 0.76

1 1.0 (0.7, 1.3) 0.9 (0.8, 1.0) 1.0 (0.8, 1.2)

0.98 0.16 0.90

1 1.9 (1.6, 2.4) 1.5 (1.4, 1.8)

o0.001 o0.001

1 1.5 (1.2, 1.9) 1.4 (1.2, 1.6)

o0.001 o0.001

0.010

1 1.0 (0.9, 1.2)

0.61

1 1.1 (0.9, 1.2)

0.34

1 3.4 (2.4, 4.9) 1.0 (0.8, 1.2) 1.6 (1.3, 1.9)

o0.001 1.00 o0.001

1 2.0 (1.3, 2.9) 0.9 (0.7, 1.1) 1.2 (0.9, 1.5)

0.001 0.22 0.27

1 1.4 (0.9, 2.1) 0.9 (0.8, 1.3) 1.0 (0.8, 1.4)

0.14 0.88 0.89

2.9 10.7 4.6

1 4.6 (3.5, 6.0) 1.7 (1.5, 2.0)

o0.001 o0.001

1 3.5 (2.6, 4.8) 1.7 (1.4, 2.2)

o0.001 o0.001

1 2.2 (1.6, 3.1) 1.5 (1.2, 2.0)

o0.001 0.001

3.8 4.0

1 1.0 (0.9, 1.2)

0.78

1 1.1 (0.9, 1.4)

0.19

1 1.2 (0.9, 1.5)

0.17

P-value

Prevalence of high psychological distress (%) Weight status BMI 18.5–24.9 BMI o18.5 BMI 25.0–29.9 BMI X30.0

36

Psychological distress determined using scores from the Kessler Psychological Distress Scale ; low ¼ 10–19 (referent), medium ¼ 20–29, high 30–50; BMI ¼ body mass index (units in kg m2, computed as weight in kilograms divided by height in meters squared). aAdjusted for each other respective risk factor. bAdjusted for each other respective risk factor plus age, gender, marital status, income, post-school education/qualification, employment status, main language spoken at home, country of birth, number of long-term medical conditions, medication use for mental well-being, smoker status, alcohol weekly consumption and leisure-time physical activity level. All covariates other than gender in adjusted analysis for medium or high psychological distress, and alcohol weekly consumption and postschool education in adjusted analysis for medium psychological distress, were statistically significant (at Po0.10 level).

International Journal of Obesity

Weight perception and psychological distress E Atlantis and K Ball

719 consistent with previous research.4,6,9,10,15,16,18 However, unlike previous research, we also considered the potential importance of weight perception and misperception in the association between obesity and psychological distress. Once considered simultaneously, effects of weight perceptions on psychological distress were substantially stronger than those for weight status and weight misperception. Overweight perception significantly increased the odds of psychological distress even after controlling for several important covariates, while associations with weight status and weight misperception were no longer significant. This subsequent finding indicates that overweight perception rather than obesity per se is associated with psychological distress. Similar and more robust results were found for underweight perception and results tended to be stronger and more consistent for high than for medium psychological stress. Results of the present study identifies subgroups of individuals at increased risk of psychological distress and suggest that inconsistencies found in the published literature relating to obesity and psychological morbidity may be due to clinical classification of weight status alone, as these studies have not accounted for weight perception. As we hypothesized, weight perceptions that deviate from societal ideals are more closely and consistently associated with psychological distress than actual weight status, regardless of weight misperception. Our findings are suggestive of an etiological link between overweight and underweight perception and an increased risk of psychological morbidity. This supports a psychosocial rather than biological explanation for psychological distress. Dysregulation of the hypothalamic–pituitary–adrenocortical system has been seen in some obese and depressed patients and has been hypothesized to be a potential cause of psychological distress, namely depression.39–41 However, the strong association between underweight perception and psychological distress observed in the present study suggests that this biological overlap is probably coincidental rather than causal, because underweight men and women across ethnic groups have very low levels of adiposity,42 and we found no documented evidence for dysregulation of the hypothalamic–pituitary–adrenocortical system in underweight– depressed patients. Studies that simultaneously measure biological and psychosocial outcomes could unravel important etiological links between weight perceptions and psychological distress. Although we acknowledge that higher levels of evidence other than cross-sectional studies are needed to confirm causality, if indeed, overweight perception leads to increases in psychological distress, plausible mechanisms should be speculated. A large literature base attests to the weightrelated stigma, discrimination and prejudice faced by obese individuals in developed countries.43 Such stigma and discrimination may serve to trigger feelings of depression among those whom recognize that their weight status does not conform to a societal ideal. Furthermore, effects of an

interaction with other unmeasured variables including low levels of self-esteem or disturbed body image may also be involved. Future research could be undertaken to test potential mechanisms of overweight perception. Implications for prevention are worthy of mention, assuming that our findings are at least partly causal in nature. Public health interventions targeting psychological distress at the population level may need to promote healthy attitudes towards body weight and self-acceptance, regardless of weight status. Clearly, both obesity and underweight are hazardous to health, increasing the risk of premature death44,45 for example. However, the notion that selfrecognition of being overweight or obese will alone reinforce the adoption of healthy behaviors is not supported. We recently documented that overweight perception among obese individuals decreased the odds for meeting recommended levels of leisure-time physical activity for health benefits, whereas acceptable weight perception among obese individuals did not, that is, rates of recommended physical activity were higher and closer to those seen among normalweight individuals, compared with overweight/obese who perceived themselves overweight.46 Second, overweight perception may serve as a barrier to participating in healthy physical activity behavior due to the feelings of being ‘too fat to exercise’.47 These findings, along with the current findings suggest that overweight perception may be linked with adverse psychological outcomes and may indicate that strategies promoting weight loss among obese individuals should also incorporate a psychosocial component focused on encouraging positive body perceptions and self-acceptance, regardless of weight status. Whether such logic could be applied for the prevention of psychological distress due to underweight perception is unknown and could be the focus of future research. Study strengths include a large, nationally representative sample, which used a well-validated psychometric scale to screen for psychological distress36,37 and adjustment for several important covariates. One obvious limitation is the cross-sectional study design, because causality cannot be determined, that is, psychological distress may cause weight perception, or weight perception may cause psychological distress. Higher levels of evidence (that is, prospective, retrospective and case–control studies) are required before the etiological role of weight perception in psychological distress can be fully ascertained. Secondly, BMI was computed from self-report height and weight values, which are associated with overestimation of height notably among shorter and older individuals for men and women, and with underestimation of weight most notably among women across the age spectrum.48 Future studies using measured height/weight data would be able to assess whether or not such self-report errors are important sources of bias when investigating psychological distress. Another potential limitation is the possible existence of unmeasured variables causally related to both weight perceptions and psychological distress. International Journal of Obesity

Weight perception and psychological distress E Atlantis and K Ball

720 In summary, weight perceptions rather than actual weight status are significantly associated with psychological distress. Individuals with weight perceptions which deviate from the societal ideal (overweight and ‘underweight) are at increased risk of psychological distress. Well-designed studies are still needed to determine whether overweight and underweight perception cause psychological distress, and if so, whether these symptoms are significantly reduced following an effective intervention.

Acknowledgements Kylie Ball is supported by a NHMRC/NHFA Career Development Award.

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