Elsevier

Appetite

Volume 59, Issue 1, August 2012, Pages 96-99
Appetite

Research report
Disinhibition is easier learned than inhibition. The effects of (dis)inhibition training on food intake

https://doi.org/10.1016/j.appet.2012.04.006Get rights and content

Abstract

Impulsivity seems to be a strong candidate when it comes to psychological factors leading to overeating and eventually to obesity (Guerrieri, Nederkoorn, & Jansen, 2008). The question is whether reversing the logic and strengthening an individual’s inhibitory skills will be equally potent against overeating. In the current study the stop signal task was adjusted so that one group of female students (n = 21) gradually got more trials in which they could practise inhibition (inhibition), whereas another group (n = 20) gradually got more trials in which they had to react quickly, without having time to think or inhibit (impulsivity). A third group (n = 20) did a neutral reading task (control). The participants in the impulsivity group had a significantly higher caloric intake during a subsequent taste test, whereas the inhibition group did not differ from the control group. Hence, the data support that impulsivity is a direct cause of overeating. However, the concept of inhibition training needs to be investigated further. Issues like the specificity of inhibition training (general vs. food specific) need to be addressed and used to optimise the training so that its effectiveness can be tested within clinical settings.

Highlights

► Impulsivity is a strong psychological factor leading to overeating and obesity. ► Training inhibition with a stop signal task should lead to less overeating. ► Training fast responses without thinking should lead to more overeating. ► Training fast responses indeed leads to overeating. ► But training inhibition does not lead to less caloric intake in the lab.

Introduction

Weight problems have become a hot topic when it comes to public health. Weight status is generally assessed by the Body Mass Index (BMI), calculated by dividing one’s weight (kg) by one’s height (m) squared. A BMI between 18.5 and 24.9 constitutes a normal weight, whereas a BMI ranging from 25 to 29.9 is defined as overweight and a BMI of 30 or more as obesity. The last decades have been hallmarked by a significant increase of overweight and obesity among children and adults (Bassett et al., 2008, Ogden et al., 2006). In the United States for example 65% of the population is overweight or obese (Hedley et al., 2004).

Finding out how obesity is caused is of paramount importance because it will help us to stop this epidemic and hence its unfavourable health, psychological and social outcomes (Hu, 2003, Karlsson et al., 2003).

Answering the question how obesity arises is not simple. There seems to be an intricate interplay between all sorts of factors: genetic, biological, psychological, environmental and sociocultural (Drewnowski, 1991, Hill and Peters, 1998, Lowe, 2003). However, before looking into interactions between causal factors, it is important that they are identified and investigated in their own right.

Based on previous research impulsivity seems to be a strong potential psychological factor (Guerrieri, Nederkoorn, & Jansen, 2008). Generally, impulsivity is defined as the tendency to think, control and plan insufficiently, resulting in an inaccurate or maladaptive response (Solanto et al., 2001). Impulsive behaviours are very diverse and include for example, sensitivity to reward and insufficient prepotent response inhibition (Guerrieri et al., 2008). In this study impulsivity was operationalised as insufficient response inhibition. Nederkoorn and colleagues were the first to link insufficient response inhibition to obesity. They found that obese children were impaired in general response inhibition, and thus impulsive, compared to control participants (Nederkoorn, Braet, Van Eijs, Tanghe, & Jansen, 2006). In other words, even on a very basic motor level that has nothing to do with food the obese children were less able to inhibit their responses. Moreover, impulsivity turned out to be an obstacle in the treatment of the obese children: the children that were worst at inhibiting responses, lost less weight (Nederkoorn et al., 2006, Nederkoorn et al., 2007). The question remained whether impulsivity directly causes overeating. As a first step the link between impulsivity and overeating was investigated within a group of healthy normal-weight women. Indeed, high impulsive women overate in the lab compared to low impulsive women, although they had a healthy weight (Guerrieri, Nederkoorn, & Jansen, 2007). As hypothesised, later experimental studies indicated that impulsivity causes overeating (Guerrieri et al., 2009, Guerrieri et al., 2007). In one study, for example, manipulating impulsivity vs. inhibition led to a higher intake of the impulsivity group in the lab compared to the inhibition group, at least for non-dieters (Guerrieri et al., 2009).

If inducing impulsive behaviour causes overeating, it could well be that training inhibition could actually protect against overeating. This has already been shown for inhibition training tasks that specifically focus on palatable food stimuli (Houben, 2011, Houben and Jansen, 2011, Veling et al., 2011, Veling et al., 2011). The study of Guerrieri et al. (2009) and the current study differ from these studies in the sense that general response inhibition skills are tackled, with the expectation that the improvement in inhibition will transfer to eating behaviour when individuals are put in a tempting food situation. This is much like general working memory trainings result in the reduction of very specific behaviours such as inattentive symptoms in children with Attention Deficit Hyperactivity Disorder (ADHD; Klingberg et al., 2005).

The results of the previous study of Guerrieri and colleagues (2009) could not be interpreted fully. There were two groups; inhibition was manipulated vs. inhibition. This only gave the opportunity to compare the mean food intake in the inhibition group with that of the impulsivity group. However, without a neutral control group, a difference in caloric intake between the inhibition and impulsivity group could be due to three different processes. There could be less intake in the inhibition group (a successful inhibition manipulation), more intake in the impulsivity group (a successful impulsivity manipulation), or a combination of both (both manipulations were successful). In other words, in order to find out whether inhibition training has any clinical relevance, we need to manipulate inhibition and compare acute caloric intake after the manipulation with intake in a neutral control group.

In sum, the current study aims not only to induce impulsivity, which is theoretically interesting in the sense that it demonstrates that impulsivity is a direct cause of overeating. If we can induce inhibition and if this induced inhibition leads to less food intake in the lab compared to the neutral control group and the impulsivity group, training inhibition becomes an option that might be clinically relevant. In other words, the hypotheses of this study are twofold. First, we expected that training participants by having them inhibit responses should lead to less caloric intake during a subsequent taste test. Second, training participants to react quickly without forethought should lead to more caloric food intake during a subsequent taste test.

Section snippets

Participants

Sixty-one normal-weight female undergraduate students (age: 21.43 years ± 2.12; BMI: 22.20 ± 2.78) were recruited to participate in a study on taste perception. Participants were randomly allocated to one of three conditions: impulsivity (20), inhibition (21), or neutral control (20). All participants were tested individually and received course credit in exchange for their participation. None of the participants was aware of the hypotheses of the study, hence the data of all participants were

Pre-existing differences between the inhibition, neutral and impulsivity group

It was checked whether the inhibition, impulsivity and neutral group differed beforehand on hunger and BMI (see Table 1 for means and standard errors per group). For this purpose two one-way ANOVA’s were conducted. The three groups did not differ significantly on hunger (F (2, 58) = 0.30; p > 0.9), nor on BMI (F (2, 58) = 0.39; p > 0.6).

Effect of inhibition/impulsivity task on caloric intake

A one-way ANOVA was conducted to check for differences in caloric intake between the inhibition, neutral and impulsivity group. The groups differed significantly in

Discussion

The aim of this study was twofold. First, we attempted to replicate the finding that impulsivity is causally linked to overeating by manipulating impulsivity. Second, we tested whether an inhibition training would decrease subsequent food intake. For this purpose participants performed one of two stop-signal tasks. In the impulsivity group the proportion of go trials gradually increased with each block, whereas this was the case for the proportion of stop trials in the inhibition group. A

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