Short communicationImpulsivity in obese women
Introduction
The incidence of obesity has increased dramatically in the past few decades. The consequences are enormous, both for obese individuals and for society. The availability of high caloric, tasty food items plays an important role; the temptation is omnipresent. However, although the relation between the increase in availability of tasty food and the increase in obesity is obvious, it cannot explain obesity on the individual level. After all, not everyone experiences difficulties in limiting one's food intake, while enduring the same food overexposure. What then makes this difference between normal weight and obese persons?
There is some evidence that obese people are more prone to give in to temptations and are less effective in inhibiting their impulses. Self-reports show that obese people are more impulsive than lean people and show co-morbidity with other impulsive behaviours, like substance abuse (Chalmers, Bowyer, & Olenick, 1990; Rydén et al., 2003; Williamson, Kelley, Davis, Ruggiero, & Blouin, 1985). In addition, it has been found that obese children are less able to delay gratification and more often choose a direct reward over a larger delayed reward, which is an index of diminished self-control (Bonato & Boland, 1983), although inconsistent results are found (Bourget & White, 1984). Recent research has also shown that obese children in a treatment programme are less effective in response inhibition in a stop signal task and are more sensitive to reward in a gamble task than lean children (Nederkoorn, Braet, Van Eijs, Tanghe, & Jansen, in press). Obese adults showed a preference for high immediate gain, but larger future losses in a gamble task, instead of lower immediate gain, but smaller future loss, indicating poor and impulsive decision making (Davis, Levitan, Muglia, Bewell, & Kennedy, 2004). Moreover, Holtkamp et al. (2004) found that children with attention deficit/hyperactivity disorder (ADHD), who are impulsive by definition, had a higher BMI and incidence of obesity, compared to reference values. Recently, co-morbidity between obesity and ADHD was reported in children (Agranat-Meged et al., 2005). Not only do obese people in general appear more impulsive, within obese individuals high impulsivity is related to less weight loss during treatment (Jonsson, Bjorvell, Levander, & Rossner, 1986; Nederkoorn, Braet, et al., in press; Nederkoorn, Jansen, Mulkens, & Jansen, in press) and is predictive of treatment drop-out (Hjordis & Gunnar, 1989).
In sum, there is growing evidence that obese people are impulsive in several aspects. However, the exact relation between impulsivity and obesity is still far from clear. Most of previous research on impulsivity and obesity relies on self-report, which is subject to demand characteristics. Behavioural research with obese adults is particularly scarce. Moreover, impulsivity is a very broad concept, incorporating many different aspects, and is defined and measured in many different ways. Correlations between these different measures of impulsivity are low (Barkley, 1991). So if it is concluded that obese people are more impulsive, what does this exactly mean?
In the present study, several measures of impulsivity will be used. One behavioural measure will be used: response inhibition as measured with the stop signal task, and three self-report measures, namely delay discounting, the trait impulsiveness of the Eysenck Personality Profiler (EPP) and sensation seeking.
Section snippets
Method
Participants were called for by advertisements in a Dutch national woman's magazine and a local newspaper, in which obese and lean women, younger than 50 years, were asked to participate. Thirty-one obese women (mean BMI 39.0, SD=5.3) and 28 normal weight women (mean BMI 22.5, SD=2.2) participated. Mean age of the normal weight group was 41.8 (SD=7.4), mean age of the obese group was 40.9 (SD=6.6; not significant ).
The stop signal task (Logan, Schachar, & Tannock, 1997) was used to
Results
The first hypothesis was that obese women show longer stop times (SSRTs), indicating a deficit in response inhibition. Overall, no significant difference was found (, ). The group×block interaction was however significant (3,55)=3.6, ), see Fig. 1. As can be inferred from the figure, both groups clearly showed a practice effect: in block 1 the SSRTs were longer than in the other blocks. While at first there was no difference between the groups, at the end of the task, the
Discussion
Obese women were expected to appear more impulsive on several measures. Indeed, the present results showed that the obese women were more impulsive on the stop signal task than the normal weight women: obese women inhibited their responses less adequately during the stop signal task in the last blocks, while they had no difficulties in responding per se. This is line with previous research, in which obese children and restrained eaters are found to show less adequate response inhibition,
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