The Restraint Model: Dieting and Disordered Eating

An important index of restrictive eating practices to have emerged from theoretical work on the phenomenon of weight control is the construct of dietary restraint. The restraint model was developed in order to explain the pathways by which dieting may be a causal factor in the development of obesity and eating disorders, and a number of theoretical mechanisms have been produced using the construct since the original use of the term in the mid 1970's (Herman and Mack 1975).

The most fundamental characteristic of restrained eaters is that they attempt to regulate and restrict their food intake using cognitive control which leads them to disregard internal cues for hunger and satiety. Restrained eaters have been demonstrated to show more sensitivity to external cues for hunger in experimental studies than non-restrained eaters ( e.g. Ogden and Wardle 1990^)Jt has been argued that this leaves them vulnerable to disinhibition, a process by which their control of their eating is disrupted, resulting in overeating. Disinhibitors which have been identified as leading to higher food consumption in restrained when compared to unrestrained eatersinclude consumption of alcohol, emotional states such as anxiety or dysphoria and cognitive factors such as the perception that they have 'broken' their diet (for a review see Ruderman 1985). The latter disinhibitor has been demonstrated in an experimental paradigm by measuring food consumption of restrained and non­ restrained eaters after a 'preload' o f a high-calorie food (or one believed by the participants to be high in calories). Whilst unrestrained eaters consume less after such a preload (regulation), restrained eaters eat more than if they had not received the preload (counter-regulation) leading to suggestions that they abandon any restraint and overeat once they perceive their eating rules to have been broken (Herman and Mack 1975, Spencer and Fremouw, 1979, Woody et al 1981). A more recent development of the restraint theory emphasises the importance of the type of restraint followed. Research by Westenhoefer and his associates has established the distinction between flexible and rigid restraint, demonstrating both psychometrically and experimentally that those whose restraint is rigid and rule-based are most prone

Chapter 3; Factors associated with weight concern and weight control

to disinhibition (Westenhoefer 1991, Westenhoefer et al 1994). Psychological characteristics of restrained eaters have also been postulated to predict diet-breaking behaviour, with particular reference to attributions related to dietary lapses. A global and internal attributional style has been found to be associated with poorer adherence to a dietary regime (Ogden and Wardle 1990^).

3.2.4.1 Restraint, dieting and binge eating

The links between restricting dietary intake and overeating have been taken a step further by Polivy and Herman (1985) who used the restraint model to implicate dieting as a causal factor in the pathogenesis of the binge eating found in both binge eating disorder and bulimia nervosa. They argue in a review of the literature, that dieting and binging frequently co-occur and that dieting usually precedes binge eating temporally, concluding that the disinhibition and counter-regulation associated with restricting food intake makes the development o f bingeing eating disturbances more likely. Whilst this model has been very influential, there has been little by way of empirical work to underpin it. The presence o f a longitudinal association between the two behaviours and the existance of a theory to postulate a relationship does not necessarily imply a direct causal relationship, since other factors could be mediating the associations. In fact in the decades since Polivy and Herman published their analysis a body of research has emerged which casts some doubt on their conclusions. Not only is dieting not a sufficient cause of bingeing, but it does not appear to be a necessary causal factor either, since some bingers have never dieted (French, Story, Downes et al 1995; Williams et al 1996). Furthermore whilst onset of dieting precedes onset o f binge eating in a majority of cases, there are a considerable minority of cases (up to 45%) in which binging precedes dieting (Haiman and Devlin 1999; Brewerton et al 2000; Bulik et al 1997; Spurrell et al 1997; Grilo and Masheb 2000).

Furthermore, in the few research papers where restraint or dieting behaviours have been examined in a mulitivariate context together with affective factors such as body dissatisfaction or depression there has been some suggestion that negative affect may

Chapter 3: Factors associated with weight concern and weight control

be a predictor of at least comparable importance. One study which used path analysis to develop a multivariate model of binge eating in obese adults (Womble et al 2001) reported that restraint and negative affect played an equally strong role in predicting binge eating. A further study by French et al (1999) found that dietary restraint was not a significant cross-sectional predictor of binge eating in multivariate analysis although depression was.

Recently a number of researchers have argued that the causal association between restraint and binge eating may have been overemphasised. Van Strien (1996) have suggested that the strong associations between restraint and bingeing found when using Herman’s restraint scale (Herman and Mack 1975; Polivy et al 1978) may be a result of the confounding within that scale of restraint and disinhibition. Studies which have used subsequently developed restrained eating scales (DEBQ: Van Strien et al 1986; and TFEQ: Stunkard and Messick 1985) which aim to distinguish between restraint and disinhibition have reported lower associations between restraint and binge eating.

Evidence for the importance o f negative affect in the pathogenesis of binge eating and bulimia has led to the development of a dual pathway model of bulimic pathology (Slice and Agras 2001; Slice et al 1998). This postulates two alternative pathways to binge eating and purging behaviours, mediated by restraint and negative affect respectively, such that either of these two factors or a combination of the two can lead to the development of binge eating. The authors of the model have reported that negative affect significantly moderates the association between dieting and binge eating in cross-sectional analyses, although not in longitudinal analyses. Lending some support to the view that affective factors play a long neglected causal role in the development of binge eating, another study (Wardle, Waller and Rapoport 2001) found that body dissatisfaction was strongly associated with binge eating in a obese women. The effect was partially mediated by depression, but not by restraint. In longitudinal analyses the greatest improvement in binge eating was found in those individuals who had become more restrained and less depressed. These findings

Chapter 3: Factors associated with weight concern and weight control

present a threat to the pre-eminence of Polivy and Herman’s theory of binge eating, and clearly indicate that the associations between dieting, body dissatisfaction, negative affect and binge eating merit further examination.