Research reportTraining inhibitory control. A recipe for resisting sweet temptations☆
Introduction
In Western societies, where palatable, high calorie food is abundantly available, the prevalence of overweight and obesity is constantly increasing (Flegal, 2005, Wang and Beydoun, 2007). As a result, more and more people attempt to control their weight through dieting. However, maintaining a successful diet is notoriously difficult, and only few dieters are able to reduce their body weight in the long term (Jeffery et al., 2000, Mann et al., 2007). This is especially true for the so-called restrained eaters, who chronically try to restrict their food intake, but who are mostly unsuccessful in their dieting attempts (Heatherton et al., 1988, Herman and Polivy, 1980) and who are more prone to overeating than unrestrained eaters (Fedoroff et al., 1997, Jansen and Van den Hout, 1991, Rogers and Hill, 1989). Thus, people in general, and restrained eaters in particular, are often tempted by their impulses to indulge in tasty, high calorie food, even though this behaviour is inconsistent with their weight control goals. What makes it so difficult to resist the temptations of high calorie food?
According to contemporary dual-process models, like the Reflective-Impulsive model (Strack & Deutsch, 2004), the outcome of such conflicts between the impulse to indulge in high calorie food and dieting standards critically depends on inhibitory control. Specifically, impulses can be overruled by higher order control processes, but only when one is able to expend enough inhibitory control resources. Indeed, research has shown that people with weaker inhibitory control eat more high calorie, palatable food (Guerrieri et al., 2009, Guerrieri et al., 2007), are more often unsuccessful dieters (Jansen et al., 2009), and are more often overweight or obese (Guerrieri et al., 2008, Nederkoorn et al., 2006, Nederkoorn et al., 2009, Nederkoorn et al., 2007) than people with more effective inhibitory control. Further, inhibitory control also interacts with dietary restraint, in such a way that especially restrained eaters are likely to overeat when they are low in inhibitory control (Jansen et al., 2009), and that food intake is more strongly related to automatic impulses and less strongly guided by dietary restraint standards when inhibitory control abilities are weak (Friese et al., 2008, Hofmann and Friese, 2008, Hofmann et al., 2009, Hofmann et al., 2007, Nederkoorn et al., 2010).
Hence, people need to recruit inhibitory capacity to override impulsive reactions to consume high calorie food. When this inhibitory capacity is insufficient, people are more susceptible to the temptations of tasty high caloric food, and they are more prone to indulge in these types of food. The present research examines whether the converse is also true: increasing inhibitory control should strengthen control over food intake, making people less vulnerable to the temptations of high calorie food and better able to restrict food intake in line with dietary standards. There is already some evidence suggesting that strengthening inhibitory control indeed decreases food consumption. Specifically, Guerrieri et al. (2009) demonstrated decreased food intake following a manipulation that primed inhibitory control compared to a manipulation that primed impulsive behaviour. However, in this study, there was no control condition, which makes it impossible to determine whether both the impulsivity and the inhibition manipulation effectively influenced food intake relative to baseline. Moreover, Guerrieri et al. primed general inhibition ability in their study and it is questionable whether such an endeavour will ultimately help people regain control over their food intake as they probably do not have a general problem inhibiting behaviour but a specific problem with resisting the temptation of palatable food.
In the present study, therefore, we examined whether practicing inhibition of food-related responses would reduce food intake relative to a control condition. In order to strengthen inhibitory control, we used a paradigm that involved repeatedly inhibiting (i.e., stopping) an approach response to stimuli. Importantly, stopping responses to stimuli in this paradigm has been demonstrated to involve motor inhibition (Veling & Aarts, in press) and effectively increases response inhibition for those stimuli that were associated with a stopping response (Verbruggen & Logan, 2008). Moreover, the same paradigm has been shown to decrease positive attitudes toward stimuli that were consistently associated with a stopping response (Houben et al., in press, Veling et al., 2008), and has even been demonstrated to facilitate behavioural changes (Houben et al., in press). Specifically, Houben et al. demonstrated that repeatedly inhibiting responses toward alcohol-related stimuli significantly reduced subsequent alcohol consumption. Based on these findings, the goal of this study was to test whether repeatedly inhibiting responses to high calorie food would decrease food intake.
Importantly, training to inhibit food-related responses should only affect eating behaviour for those experiencing strong impulses to indulge in certain types of food. Therefore, we selected a sample of trait chocolate cravers who experience intense and frequent cravings for chocolate (Benton, Greenfield, & Morgan, 1998). Participants were randomly assigned to one of three conditions: in the control condition, participants were allowed to respond to chocolate on half the trials, while they had to inhibit their responses on the other half of the trials. In contrast, in the experimental chocolate/no-go condition, participants had to consistently inhibit their responses to chocolate. It was expected that strengthening inhibitory control toward chocolate in this way would decrease the consumption of chocolate during a subsequent taste test relative to the control condition. Further, it was expected that chocolate consumption would be more strongly guided by dietary restraint standards in the chocolate/no-go condition than in the control condition. Finally, we also included a chocolate/go condition, in which participants consistently had to respond to chocolate to examine whether such a manipulation would in fact increase impulsive chocolate consumption and would decrease dietary control over chocolate consumption.
Section snippets
Participants
Sixty-nine female undergraduate students (age: M = 20.08, SD = 2.25) participated in this study. Participants were screened with the Attitudes to Chocolate Questionnaire (ACQ; Benton et al., 1998) 1–2 weeks before the study. The chocolate craving subscale of the ACQ consists of 10 items that measure the amount of chocolate craving with higher scores indicating stronger chocolate craving. Every item of the craving subscale presented a statement regarding the experience of craving for chocolate.
Results
Four participants correctly guessed the goal of the go/no-go manipulation and were therefore removed from the sample. In addition, two outliers with a chocolate consumption that was 2.5 SD above the mean chocolate consumption were also removed from the sample. The final sample consisted of 63 participants, divided over the go/no-go control condition (n = 22), the chocolate/no-go condition (n = 21) and the chocolate/go condition (n = 20). There were no significant differences in age, BMI, or restraint
Discussion
The present study examined whether training inhibition of food-related responses effectively increases control over food intake so that consumption of high calorie food is more in line with dietary restraint standards. Specifically, as a first attempt to test this hypothesis, the inhibition training aimed to increase control over chocolate consumption in a sample of trait chocolate cravers. As expected, participants who consistently had to inhibit their responses to chocolate stimuli in the
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This research was supported by a grant from the Technology Foundation STW.