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Research in implicit food attitudes has addressed both a) attitudes towards food (sometimes relative to pleasant non-food stimuli), and b) attitudes towards certain food types, relative to other food types. If ego depletion can partially account for disinhibited eating in dieters or restrained eaters, then we might expect to see no differences in implicit food attitudes between restrained and unrestrained participants. Specifically, we might expect both restrained and unrestrained eaters to hold positive implicit attitudes with high-fat, high-sugar, and/or high-carbohydrate foods. In line with this explanation, dietary restraint failure would occur when self-control resources are depleted by restraint, causing the person to behave more impulsively and indulge in foods with which they hold positive automatic associations.

Unrestrained eaters do not engage in dietary restraint and therefore are less likely to be in a state of ego depletion which would result in this type of impulsive eating. The empirical evidence partially supports this explanation; however, the findings have not been unequivocal.

Several studies which have contrasted restrained and unrestrained eaters found that both groups held positive implicit associations with food. Participants in a study by Veenstra and de Jong (2010) completed an Affective Simon Task to respond to high-fat and low-fat food images and “Tasty” or “Non-tasty” vocal responses. A “manikin” version of the task, in which

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participants moved a mannequin figure towards or away from stimuli, was also included as a measure of automatic approach or avoidance. Participants were classified as restrained or unrestrained eaters on the basis of scoring in the top or bottom quartile, respectively, of the Restraint Scale (Herman & Polivy, 1980). Both restrained and unrestrained eaters held more positive associations with high fat, compared to low fat, food. However, restrained eaters had stronger automatic approach tendencies for high fat foods3_{. These findings are apparently}

consistent with the ego depletion account of dietary restraint failure. Roefs, Herman, MacLeod, Smulders and Jansen (2005) found similar results. In Experiment 1, restrained and unrestrained female participants completed an Affective Priming Task using pictures of high-fat and low-fat food, and general positive and negative words. Both participant groups held stronger positive associations with high-fat food. In Experiment 2, restrained and unrestrained participants completed the EAST using high-fat and low-fat food words, and “Palatable” or “Unpalatable” words. No differences were found between groups; however, there was also no effect of fat content on response. Papies, Stroebe and Aarts (2009) found, using an Affective Priming Task, that unrestrained eaters held a stronger preference for high-fat, compared to low-fat food. Restrained eaters did not hold a preference for either food type, although associations in both groups were positive towards both food types.

One study has carried out an experimental study of the effects of restraint on implicit attitudes. Hoefling and Strack (2008) contrasted implicit food associations using the EAST in fasting (for 15 hours) versus non-fasting, and in restrained versus unrestrained participants. A main effect of group was found; fasting participants held more positive associations with all food words compared to the non-fasting group. A marginally significant interaction between restraint status and calorie content was found; restrained participants held slightly stronger positive associations with high-calorie foods than the unrestrained. These findings suggest that the act of fasting may actually change the pattern of implicit food associations: i.e., inflate the positive associations with high-calorie foods. However, a longitudinal replication study with at

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least two time points would be necessary to support this hypothesis (see Study 4). The ecological validity of the Hoefling and Strack (2008) study is somewhat limited because most restrained eaters do not tend to fast for extended periods of time, but rather change the amount or content of what they eat. Moreover, the fasting was motivated by study participation, rather than an internal weight loss goal.

By contrast, research which has used the IAT has not supported a universal positive implicit attitude towards high-calorie foods. Maison, Greenwald and Bruin (2001) assessed positive and negative associations with high-calorie and low-calorie foods. A main effect of calorie content was found: participants held stronger positive associations with low-calorie, compared to high-calorie, foods. Although apparently some differences between restrained and unrestrained eaters were found, these were not reported. Regardless, if a preference for high- calorie foods is not normative, then the ego depletion hypothesis cannot explain why dieters choose to binge on cake or crisps rather than, for example, celery. Similarly, Roefs and Jansen (2002) contrasted high-fat and low-fat food associations in obese versus normal weight participants using the IAT. Both groups held stronger negative associations with high-fat food. Although this may be interpreted as an absolute negative attitude, it is possible that including low-fat foods in the dataset increases the salience of health during assessment and decreases positive associations with high-fat foods. It is also worth noting that both of these studies used general “Positive” or “Negative” words for the valence category. The results can therefore be interpreted as participants’ associations between food and their global positive or negative value; this approach would be expected to yield different results patterns than studies which assess implicit associations between different food types and tastiness, or food and healthiness.

While the findings may appear contradictory on the surface, a study by Houben, Roefs and Jansen (2010) has highlighted the importance of methodology in this type of research. Restrained eaters’ attitudes towards high-calorie and low-calorie foods were assessed in two studies: one using a standard “relative” IAT assessment, and the other using a non-relative, “single category” IAT variant. The single category variant is methodologically more similar to

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measures such as the AST and the EAST because they measure non-relative associations. The studies found that when the standard, relative IAT measure was used, there were no significant differences in implicit food attitudes between restrained and unrestrained eaters. However, when attitudes were assessed using the single-category variant, restrained eaters had stronger positive associations with high-fat foods, compared to the unrestrained. These findings may be explained by research on the effects of context in implicit attitude research, and by parallel distributed processing approaches to implicit cognition: including different food categories could have an effect on the types of associations which are activated (and therefore measured).

In addition to the differences in relative versus non-relative assessment, the implications of using global or specific variables as the valence stimuli are also important. The role of ambivalence towards food in restrained eaters has already been discussed; people who consciously try to restrict their diet tend to have mixed feelings about high-fat or high-calorie foods (Urland & Ito, 2005). While it has not been addressed experimentally, it is not impossible that such ambivalence might also be reflected on an implicit level. In line with the spreading activation approach to implicit cognition (such as the REC model), “cake” may be associated with several concepts, including those with seemingly contradictory valences – such as “tasty” and “fattening”. The former is more likely to play a role in restraint failure, given that impulsive eating behaviour is thought to be driven by the anticipation of a hedonic reward. It can

therefore be reasonably hypothesised that the strength of this association would also result in stronger craving and thus a lower rate of restraint success. Alternatively, perhaps there are individual differences in the experience of ego depletion which can lead to restraint failure in some people, but not others, despite similarities in their implicit attitudes towards food.

4.2. IN EATING DISORDERS

Perhaps surprisingly, very little research in implicit food attitudes has been carried out in clinical ED populations. One study by Roefs et al. (2005) found, using an Affective Priming Task

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(high-fat vs. low-fat foods, palatable vs. unpalatable), that healthy controls held stronger implicit positive associations with high-fat food, compared to low-fat food. Those diagnosed with AN or EDNOS, by contrast, did not have stronger associations with either food type. Given how “successful” people with AN are at dietary restriction, these findings – while very

preliminary – are consistent with the ego depletion account of dietary restraint success. If those with AN do not have an implicit preference for high-fat foods then they will presumably

experience a less strong impulse to indulge in them, even when in a state of ego depletion. This is consistent with self-report and biological data which suggests that taste is impaired to some extent in AN (Casper, Kirschner, Sandstead, Jacob, & Davis, 1980; Simon, Bellisle, Monneuse, Samuel-Lajeunesse, & Drewnowski, 1993). Of course, anhedonia in and of itself can explain why dietary restriction is relatively easier in AN, but if similar associations are present on an implicit level they can explain why people with AN continue to be successful even when their self- control resources are depleted.

By contrast, people with BN report an enhanced hedonic experience of food, particularly of sweetness (Drewnowski, 1987; Franko, Wolfe, & Jimerson, 1994). Again, this very likely plays a role in bingeing behaviour, but it is unclear whether positive implicit attitudes towards high- calorie foods also contribute to restraint failure. Restrained eaters are behaviourally similar to those with BN in the sense that both repeatedly attempt, and fail, to restrict their dietary intake. The majority of research discussed above suggests that restrained and unrestrained eaters hold more positive associations with high-fat or high-calorie than with low-fat or low- calorie foods. The ego depletion hypothesis, if it is supported, can partially explain why

restriction often fails in both BN and restrained eaters: dietary restraint leads to ego depletion, which leads to more impulsive behaviour, driven by positive associations with “forbidden” foods. In AN, this behaviour is potentially curtailed by some extent by a lack of such positive associations. In BN, it is possible that such associations are enhanced. Alternatively, there may be differences in the extent to which dietary restraint contributes to a state of ego depletion in people with AN versus in those with BN.

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As discussed in section 1.4 of this chapter, the terms “restriction”, “restraint”, and “dieting” have different implications depending on the population in which they are discussed. For instance, caloric restriction in AN is a pathological and harmful behaviour, while this may not necessarily be the case for someone of who is overweight. Restraint as defined by Herman and Polivy (1980) is technically not “applicable” to AN, as anorectics are extremely successful at reducing their food intake. The present study, and subsequent studies in this Thesis, were all conducted on non-clinical participants who were, on average, of a normal weight. The terminology and discussion is therefore appropriate to those participant samples, and should not be extrapolated to clinical or obese samples. However, ED symptomatology is discussed in terms of sub-clinical, but elevated levels. High-pathology participants are typically more similar to the “unsuccessful” restriction associated with BN; however, Study 4 will also focus on “successful dieters”, whose behavioural features resemble the “success” of AN more closely than they do BN. Despite the fact that the outcomes of non-clinical studies cannot be

generalised to clinical samples, EDs and ED studies are still discussed throughout, as it is helpful to consider the findings within a broader context of the full spectrum of ED pathology.