COMMENTARY

Undue Influence of Weight on Self-Evaluation:A Population-Based Twin Study of Gender

Differences

The sheer size of this study is awe inspiring: 8,045 same-sex and opposite-sex Norwegiantwins were studied, ranging in age from their late teens to their early thirties and recruitedfrom a population-based twin registry. As yet, this is the biggest ever twin study to examineaspects of eating disorders (Reichborn-Kjennerud et al., 2004). Conducting a study of thissize in itself is a major feat and must require phenomenal logistical and strategic skills.Moreover, a population-based sample of this size has the potential of overcoming theproblem of limited power that has bedeviled earlier twin studies.

So, what is the article about? First, it explores the extent to which genetic and environ-mental factors contribute to men’s and women’s liability to putting undue importance onweight as an indicator of self-evaluation. Second, it determines whether differences existbetween males and females in the nature and magnitude of the contribution of thesegenetic and environmental factors.

Subjects were sent a questionnaire which contained, among other things, a handful ofquestions about eating disorders. One of these questions i.e. (Is it important for your self-evaluation that you keep a certain weight?) forms the basis of the current analysis. Thisquestion directly paraphrases one of the criteria for both anorexia nervosa and bulimianervosa outlined in the 4th ed. of the Diagnostic and Statistical Manual of MentalDisorders (DSM-IV; American Psychiatric Association, 1994). Self-evaluation is a rathercomplex concept and I wonder how well people understand this question without anyfurther explanation or probes. Even if people do understand the meaning of the conceptof self-evaluation, the question is rather ambiguous and one can approach it in differentways. It could be approached from a position of not wanting to lose weight or notwanting to gain weight. Do men and women approach the question in the same way?We just do not know. Clearly, this is a somewhat blunt instrument, necessitated undoubt-edly by limitations on the number of questions the researchers were able to put to theprecious twin sample. No attempt was made to assess the temporal stability of theanswer or to get participants to consider a time scale (current, life-time) for the question.

I did feel somewhat reassured by the validation exercise the authors performed. Itshowed significant associations between the ‘‘undue influence of weight on self-evaluation’’question and other eating disorder symptoms and DSM-IV criteria for eating disorders.

The main findings of the study are based on a structural equation modeling analysis.The analysis suggests that shared environmental factors account for approximately onethird of the variability in undue influence of weight on self-evaluation, whereas non-shared environmental factors account for two thirds, with no clear gender differences.These findings concur with those of a much smaller, but carefully conducted, study byWade, Martin, and Tiggemann (1998) in female twins. The earlier study used subscales of

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the Eating Disorders Examination (EDE; Cooper, Cooper, & Fairburn, 1989). They foundthat the EDE subscales Dietary Restraint, Eating Concern, and Shape Concern were bestexplained by additive genetic effects and nonshared environment, whereas the EDEsubscale of Weight Concern, which encompasses the area of undue influence of weighton self-evaluation, was best explained by shared and nonshared environments.

So, what is new? Haven’t we known all along that the undue influence of weight onself-evaluation or weight concerns are environmentally determined? Sociocultural andhistorical researchers might say, ‘‘We told you so.’’ Studies of historical sources on eatingdisorders suggest that undue influence of weight on self-evaluation or weight concernswere not part of the earliest presentations of these disorders. The first clinical descriptionof an eating disorder subject placing undue influence on weight for self-evaluation datesback to the famous case of the French psychiatrist, Charcot. He discovered that one of hisyoung female patients had put a rose-red ribbon around her waist because she did notwant to become fat like her ‘‘maman.’’ Careful crosscultural work, such as that of Becker,Burwell, Gilman, Herzog, and Hamburg (2002) in Fiji, has demonstrated the develop-ment of de novo weight concerns in young women after the introduction of Westerntelevision into this traditional society. There are many other similar examples.

Perhaps, the ‘‘haven’t we known this all along’’ position is not quite fair. For manyyears, it was dogma that anorexia and bulimia nervosa were a product of Westernsocietal influences (Littlewood, 1990). Behavioral geneticists, as well as the authors ofthe current article, helped to challenge this view. An impressive and growing body oftwin studies has demonstrated that there is considerable genetic liability to the develop-ment of both anorexia nervosa and bulimia nervosa and that some eating disordersymptoms such as binging and vomiting are highly heritable (Bulik, Sullivan, Wade,and Kendler 2000). A genetic mutation associated with binge eating has now been found(Branson et al., 2003). The findings of the current study need to be considered against thebackground of growing evidence that familial resemblance in twins for the full eatingdisorder syndromes and many core symptoms is best explained by additive geneticfactors and unique environmental factors.

What is tantalizing is that the study does not shed any light on the nature of thecommon (or nonshared) environmental effects. The authors point out that a lot ofdifferent things can be subsumed under common environment, such as intrafamilialenvironmental factors, media influences, or peer relationships. In this context, we mustnot forget that a wealth of studies exist which have produced in-depth information aboutprecisely how these heterogeneous factors might influence the development of differentbehavioral and attitudinal eating disorder symptoms, including weight concern (for areview, see Stice, 2002; van den Berg, Thompson, Obremski-Brandon, & Coovert, 2002). Itis beyond the scope of this commentary to review these in any detail.

In the area of intrafamilial influences, community-based case-control studies (Fairburnet al., 1999) identified the significance of critical comments made by family membersconcerning weight, shape, and eating as a risk factor for bulimia nervosa. In the area ofmedia influences, studies have documented the impact of reading magazine articlesabout dieting on adolescent boys and girls (Utter, Neumark-Sztainer, Wall, & Story,2003), the effects of viewing images of thin women (Groesz, Levine, & Murnen, 2002)or muscular men (Leit, Gray, & Pope, 2002), and the impact of thin fashion models(Tiggemann, Gardiner, & Slater, 2000). There are also studies on television watchinghabits or watching music videos (Tiggemann & Pickering, 1996). In the domain of peerrelationships, attitudes within friendship cliques contribute significantly to the predictionof female adolescents’ body image concerns and eating behaviors. These attitudes may be

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communicated through group talk and teasing (Paxton, Schutz, Wertheim, & Muri, 1999).In a recent experimental study, brief exposure to ‘‘fat talk,’’ that is, a thin attractivefemale complaining about how fat she feels and how she needs to lose weight, resulted inincreased body dissatisfaction in undergraduate women (Stice, Maxfield, & Wells, 2003).

Perhaps, it is a bit like this: Population-based twin studies are like blockbuster movies,big and bold, cleverly done, and not concerned with subtle detail, whereas some of theother research studies on common environment are more comparable to art housemovies, that is, intricate, in depth, and detailed. As an avid cinema goer, I like both.

REFERENCES

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.).Washington; DC: Author.

Becker, A.E., Burwell, R.A., Gilman, S.E., Herzog, D.B., &Hamburg, P. (2002). Eating behaviours and attitudes follow-ingprolongedexposure to televisionamongethnicFijianadolescentgirls.British JournalofPsychiatry,180,509–514.

Branson, R., Potoczna, N., Kral, J.G., Lentes, K.U., Hoehe, M.R., & Horber, F.F. (2003). Binge eating as a majorphenotype of melanocortin 4 receptor gene mutations. New England Journal of Medicine, 348, 1096–1103.

Bulik, C.M., Sullivan, P.F., Wade, T.D., & Kendler, K.S. (2000). Twin studies of eating disorders: A review.International Journal of Eating Disorders, 27, 1–20.

Cooper, Z., Cooper, P.J., & Fairburn, C.G. (1989). The validity of the Eating Disorder Examination and itssubscales. British Journal of Psychiatry, 154, 807–812.

Fairburn, C.G., Cooper, Z., Doll, H.A., & Welch, S. L. (1999). Risk factors for anorexia nervosa. Three integratedcase-control comparisons. Archives of General Psychiatry, 56, 468–476.

Groesz, L.M., Levine, M.P., & Murnen, S.K. (2002). The effect of experimental presentation of thin media imageson body satisfaction: A meta-analytic review. International Journal of Eating Disorders, 31, 1–16.

Leit, R.A., Gray, J.J., & Pope, H.G. Jr. (2002). The media’s representation of the ideal male body: A cause formuscle dysmorphia? International Journal of Eating Disorders, 31, 334–338.

Littlewood, R. (1990). From categories to contexts: A decade of the ‘‘new cross-cultural psychiatry.’’ BritishJournal of Psychiatry, 156, 308–327.

Paxton, S.J., Schutz, H.K., Wertheim, E.H., & Muri, S.L. (1999). Friendship clique and peer influences on bodyimage concerns, dietary restraint, extreme weight-loss behaviors, and binge eating in adolescent girls.Journal of Abnormal Psychology, 108, 255–266.

Reichborn-Kjennerud, T., Bulik, C.M., Kendler, K.S., Roysamb, E., Tambs, K., Torgersen, S., & Harris, J.R. (2004).Undue influence of weight on self-evaluation: A population-based twin study of gender differences. Inter-national Journal of Eating Disorders, 35, 123–132.

Stice, E. (2002). Risk and maintenance factors for eating pathology: A meta-analytic review. PsychologicalBulletin, 128, 825–848.

Stice, E., Maxfield, J., & Wells, T. (2003). Adverse effects of social pressure to be thing on young women: Anexperimental investigation of the effects of ‘‘fat talk.’’ International Journal of Eating Disorders, 34, 108–117.

Tiggemann, M., & Pickering, A.S. (1996). Role of television in adolescent women’s body dissatisfaction and drivefor thinness. International Journal of Eating Disorders, 20, 199–203.

Tiggemann, M., Gardiner, M., & Slater, A. (2002). ‘‘I would rather be size 10 than have straight A’s.’’ A focusgroup study of adolescent girls’ wish to be thinner. Journal of Adolescence, 23, 645–659.

Utter, J., Neumark-Sztainer, D., Wall, M., & Story, M. (2003). Reading magazine articles about dieting andassociated weight control behaviors among adolescents. Journal of Adolescent Health, 32, 78–82.

van den Berg, P., Thompson, J.K., Obremski-Brandon, K., & Coovert, M. (2002). The tripartite influence model ofbody image and eating disturbance: A covariance structure modeling investigation testing the mediationalrole of appearance comparison. Journal of Psychosomatic Research, 53, 1007–1020.

Wade, T., Martin, N.G., & Tiggemann, M. (1998). Genetic and environmental risk factors for the weight andshape concerns characteristic of bulimia nervosa. Psychological Medicine, 28, 761–771.

Ulrike SchmidtSection of Eating DisordersP.O. Box 59Institute of PsychiatryDe Crespigny ParkLondon SE5 8AF UKDOI: 10.1002/eat.10259

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