خویشتن داری غذایی و عزت نفس بعنوان پیش بینی کننده افزایش وزن در طول یک دوره 8 ساله

Abstract The study aimed to assess dietary restraint and self-esteem as predictors of weight change over a time period of 8 years. Questionnaires assessing self-reported weight, body dissatisfaction, dietary restraint, and self-esteem were completed by 77 young adults (19 men and 58 women) on two occasions separated by 8 years. On average, participants gained approximately 6 kg over the 8 years. Although neither dietary restraint nor self-esteem predicted weight change on its own, their interaction did. Furthermore, the relationship between restraint and weight change was best described as curvilinear. It was concluded that dietary restraint is predictive of subsequent weight gain, but in a more complex way than previously assumed.

A number of studies document that many women experience considerable dissatisfaction with their body size and shape, and that such body dissatisfaction seems remarkably stable across the female adult life span (Tiggemann & Lynch, 2001). For men, there is evidence that body dissatisfaction seems to increase with age (e.g., Rozin & Fallon, 1988). Nevertheless, adults (both men and women) typically put on weight as they age Andres, 1989 and Heatherton et al., 1997. Such weight gain may move individuals into the overweight or obese categories, with the attendant potentially negative health consequences. As yet, however, there has been relatively little investigation of the predictors (other than age) of such weight gain. In one recent study, Quatromoni, Copenhafer, D'Agostino, and Millen (2002) found that women who consumed a diet high in empty calories were more at risk of overweight over a 12-year period than those who consumed a heart-healthy diet. Similarly, Ball, Brown, and Crawford (2002) found that women who gained weight over 4 years had greater sitting time and consumed take-away food more frequently than weight maintainers. One common response among women to body dissatisfaction and anticipated weight gain is to diet to reduce (or maintain) weight. Correspondingly, the prevalence of dieting is now so great that Polivy and Herman (1987) argue that normal eating for women in Western countries is characterised by dieting. Yet, it is clear that diets rarely work (Herman & Polivy, 1991). Furthermore, dieting is argued to be counterproductive. Restraint theory (Herman & Polivy, 1991) suggests that when restricted eating practices (diets) are violated, chronic dieters will actually eat more than they normally would. Thus, restricted eating practices may lead to subsequent binging and have been implicated in the eating disorders of anorexia nervosa and bulimia Polivy & Herman, 1985 and Striegel-Moore et al., 1986. Although Heatherton, Herman, Polivy, King, and McGree (1988) have argued that dieters are not particularly successful at losing weight because they vacillate between periods of intense calorific restriction and bouts of disinhibited eating, which tend to cancel each other, thereby precluding weight loss, few studies have explicitly examined the relationship between dietary restraint and body weight. Heatherton, Polivy, and Herman (1991) found that a small sample of chronic dieters displayed greater weight fluctuations over a period of 6 weeks than did nondieters. There was no weight change in either group over a 6-month time period. Among larger samples of college students, Klesges, Klem, Epkins, and Klesges (1991) and Tiggemann (1994) similarly found no relationship between restraint and weight change over 2 1/2-year and 7-month time periods, respectively. In the latter study, restrained eaters reported both more recent weight loss and more recent weight gain than unrestrained eaters did. On the other hand, Klesges, Isbell, and Klesges (1992) found that weight gain was associated with higher restraint for women, but not for men, over a 1-year period. For middle-aged samples, French et al. (1994) found that a history of dieting (restraint was not measured) predicted weight gain in both men and women over a 2-year period, while Juhaeri et al. (2002) found greater weight gain over a 6-year period for self-identified dieters than for nondieters. Finally, Stice, Cameron, Killen, Hayward, and Taylor (1999) found that although restraint did not predict growth in relative weight among adolescent girls, it did predict increased hazard for obesity over a 3-year period. Although Stice et al. (1999) argue that the differences in results of different studies are largely due to differences in statistical power, there are other possible explanations for the equivocal results, including the use of different measures, samples, and time periods. A further possibility that other individual differences may play a moderating role is suggested by the results of laboratory studies that have generally shown different eating patterns for dieters and nondieters. In particular, dietary restraint predicts increased food consumption in response to a number of identified disinhibitors, for example, calorific preload (Herman & Mack, 1975), alcohol (Polivy & Herman, 1976), negative affect (Schotte, Cools, & McNally, 1990), depression (Baucom & Aiken, 1981), ego threat (Heatherton, Herman, & Polivy, 1991), and distraction (Boon, Stroebe, Schut, & Ijntema, 2002). However, not all dieters react to disinhibition by eating. For example, Kirschenbaum and Dykman (1991) found that restrained eaters with high self-control skills ate more than those with low self-control skills following a milkshake preload. In contrast, Polivy, Heatherton, and Herman (1988) demonstrated that only low-self-esteem participants disinhibited following a milkshake preload. Restrained eaters with high self-esteem did not show this counterregulatory response. This result has been replicated for distress as a disinhibitor (Heatherton et al., 1991). Thus, the aim of the present study was to further investigate the relationship between dieting and weight over a longer period of time than in the previous studies. In particular, the present study examined both dietary restraint and self-esteem as predictors of weight change over a time period of 8 years.

3. Results 3.1. Change over time A series of 2×2 mixed design ANOVAs was conducted, with time as the repeated measure and gender as the between-subjects variable. Table 1 displays the means for all variables at Times 1 and 2 for women and men, separately. Table 1. Mean scores (S.D. in parentheses) for Times 1 and 2 for men and women Time 1 Time 2 Weight Men 75.2 (6.2) 81.6 (10.2) Women 58.0 (7.0) 64.2 (10.0) Perceived weight Men 4.1 (0.9) 4.5 (1.1) Women 4.8 (1.0) 4.8 (0.9) Weight satisfaction Men 4.5 (1.6) 4.4 (1.7) Women 3.5 (1.3) 3.6 (1.4) Perceived overweight (%) Men 3.4 (9.9) 3.6 (5.6) Women 7.0 (6.2) 9.7 (7.6) Restraint Men 9.6 (4.8) 10.3 (6.0) Women 14.3 (6.2) 14.5 (5.6) Self-esteem Men 41.8 (4.7) 44.5 (3.3) Women 38.9 (6.6) 42.2 (5.6) Table options For weight, there was a significant effect of gender, F(1,70)=63.08, P<.001, and a significant effect of time, F(1,70)=55.58, P<.001. There was no significant interaction between gender and time, F(1,70)<1, P>.05. From Table 1, it can be seen that both men and women gained weight over the 8-year time period, with men gaining an average of 6.39 kg (S.D.=5.46) and women gaining an average of 6.15 kg (S.D.=6.39). There were significant gender effects on all the body dissatisfaction measures, whereby women rated themselves as more overweight, F(1,75)=5.50, P<.05, expressed greater weight dissatisfaction, F(1,74)=6.93, P<.01, and wished to be thinner, F(1,63)=7.29, P<.01. None of the time or Time×Gender effects proved significant (all Ps>.05). Thus, body dissatisfaction remained stable over the 8-year time period. Women scored higher than men did on dietary restraint, F(1,68)=9.51, P<.01, with no significant change over time for men or women, as indicated by the lack of a significant main effect of time or interaction with gender (Ps>.05). For self-esteem, men scored higher than women did, F(1,74)=4.06, P<.05, and both sexes' scores increased over time, F(1,74)=15.23, P<.001, with no significant Gender×Time interaction. In summary, both men and women put on weight over an 8-year time period, but did not change in their degree of body dissatisfaction and dietary restraint, and increased their self-esteem levels. This pattern is consistent with the results of within-time regression analyses, which showed that the three body dissatisfaction measures predicted self-esteem at Time 1, F(3,63)=6.83, P<.001, but was no longer the case at Time 2, F(3,66)=1.28, P>.05. 3.2. Restraint and self-esteem as predictors of weight change To assess restraint and self-esteem as predictors of weight change, hierarchical multiple regressions were conducted for men and women separately, with weight at Time 2 as the outcome variable. Weight at Time 1 was entered on Step 1, followed by dietary restraint and self-esteem on Step 2, followed by the product term on Step 3. A significant interaction is indicated when the product term offers unique prediction over and above that contributed by the main effects. For men, neither of the variables entered in Step 2, change F(2,14)<1, P>.05, nor in Step 3, change F(1,13)=2.48, P>.05, offered any prediction. For women, on the other hand, while the individual variables were not significant, change F(2,49)<1, P>.05, the Restraint×Self-esteem product term, did offer additional prediction, change F(1,48)=8.80, P<.01. To describe the form of the significant Restraint×Self-esteem interaction for women, the sample was dichotomized into low and high self-esteem on the basis of a median split (cut-off between 39 and 40) and low and high dietary restraint on the basis of a median split (cut-off between 13 and 14). Table 2 presents the weights at Times 1 and 2 for the four resulting groups. It can be seen that while all groups put on weight, the groups who put on the most weight were those low or high in both dietary restraint and self-esteem. The group who put on the least weight were those low in dietary restraint and high in self-esteem. Table 2. Weights at Times 1 and 2 for low and high self-esteem and dietary restraint groups of women Time 1 Time 2 Change Lo Rest–Lo S-E 53.7 (6.8) 61.4 (8.0) 7.7 (6.6) Lo Rest–Hi S-E 59.1 (6.1) 64.0 (8.9) 4.9 (4.4) Hi Rest–Lo S-E 59.1 (7.3) 64.7 (11.7) 5.6 (7.6) Hi Rest–Hi S-E 60.3 (6.9) 67.5 (11.1) 7.1 (6.6) Table options 3.3. Differences between weight-change groups On the basis of weight change over the 8 years, participants were divided into three groups: those who had lost weight (8%, n=6: 1 man, 5 women), those who had maintained weight, defined as having gained 0 to 3 kg (31%, n=22: 6 men, 16 women), and those, the majority, who had put on (more than 3 kg) weight (61% n=43: 11 men, 32 women). The weight change distribution did not differ by gender, χ2(2)<1, P>.05. The analyses of the Time 1 variables showed that these three groups did not differ significantly in age, F(2,68)<1, P>.05, initial weight, F(2,68)<1, P>.05, nor any of the body dissatisfaction measures [perceived weight, F(2,68)=1.66, P>.05; weight satisfaction, F(2,67)=1.30, P>.05; perceived overweight, F(2,65)=2.05, P>.05]. The difference approached significance on self-esteem, F(2,68)=2.90, P<.10, whereby those who subsequently lost weight tended to have had lower self-esteem (M=34.3) than those who maintained (M=41.1) or gained weight (M=39.5). Finally, there was a significant difference between groups on dietary restraint, F(2,68)=3.65, P<.05. As can be seen in Table 3, which provides the mean Time 1 scores on restraint for the three weight change groups, those few people (n=6) who lost weight did have the highest restraint scores, but those who gained weight had higher restraint scores than weight maintainers had. Table 3. Mean scores on restraint for those who lost weight, maintained, or put on weight Lost weight (n=6) Maintained weight (n=22) Gained weight (n=43) Restraint Men 11.0 (0.0) 7.8 (3.0) 11.9 (5.1) Women 19.2 (11.5) 12.1 (5.2) 14.1 (5.4) Total 17.9 (10.8) 10.9 (5.0) 13.5 (5.3) Table options Such a pattern suggests the possibility of nonlinear effects. This was more formally tested for the continuous weight change variable across the entire sample by hierarchical multiple regression. Weight at Time 2 was the outcome variable, with restraint (linear component) entered on Step 1, and restraint squared (quadratic component) entered on Step 2. As before, the linear component was not significant, change F(1,68)<1, P.>05. However, the quadratic component did provide significant prediction, change F(1,67)=4.09, P<.05. Thus, the relation between dietary restraint and weight change is best described by a curvilinear relationship, whereby dietary restraint is related positively to weight gain, except for those people very high in restraint who tend to lose weight.