Impulsivity predicts treatment outcome in obese children

Abstract

Treatment for obesity is still running short, particularly on the long term. However, some people do take advantage of treatments and are able to retain their weight loss. What makes the difference between those who can keep their weight loss and those who cannot? One possible predictor of relapse in obesity treatment is impulsivity. Overall, obese people are found to be more impulsive than lean people, especially obese binge eaters. Intuitively, it would make sense that the most impulsive people are less able to keep control over eating behaviour. Therefore, impulsivity could serve as an obstacle for treatment. In the present study impulsivity was measured with a behavioural task (the stop signal task) in 26 obese children. Overweight of the children was measured before and after treatment and at 6 and 12 months follow ups. The results show that impulsivity was related to overweight at all moments: The most impulsive children were the most overweight ones; even after 12 months. Moreover, impulsivity predicted therapy success: the most impulsive children lost less weight. Impulsivity appears to contribute to the difference between succeeding or failing in attempts to lose weight.

Introduction

Obesity is a growing problem over almost the entire world and much effort is invested nowadays in both prevention and treatment. However, the results of behavioural interventions are disappointing. Although reasonable effects are achieved at the short term, about 5 to 15% reduction of Body Mass Index (BMI, kg/m²), most people fail to stabilize their new weight. Reviews show that after 1–5 years, the majority of obese individuals returned to or exceeded their initial BMI (e.g. Garner & Wooley, 1991; Jeffery et al., 2000; Wadden, Sternberg, Letizia, Stunkard & Foster, 1989). The figures in children are more optimistic (Epstein, Valoski, Kalarchian, & McCurley, 1995), which may have several causes: parental support, children being less set in their habits, children having more structured opportunities to exercise and sport and, last but not least, children growing whereas their body composition is still changing (Epstein et al., 1995). Epstein and colleagues reported that after 6 months of cognitive behavioural treatment, almost half of the children had an impressive outcome of at least 20% reduction in overweight, while after 10 years almost 30 percent retained this large reduction. However, not all children were this successful and a large proportion (exact numbers are not revealed) had no reduction or even gained in overweight. As shown, the variability in weight loss after treatment is large. Some people can retain their weight loss, others just cannot. This means that some children apparently are able to make life-style changes and alter their eating and activity patterns, while others are not. But what makes the difference? This is an important question in order to improve therapy and let more obese children profit.

One possible predictor of relapse in obesity treatment is impulsivity. Overall, obese people are found to be more impulsive than lean people, especially obese binge eaters (Davis, Strachan, & Berkson, 2004; Nederkoorn, Braet, Van Eijs., Tanghe, & Jansen, in press; Rydén et al. (2003), Rydén et al. (2004)). Intuitively, it would make sense that the most impulsive people are less able to retain control over eating behaviour and are more inclined to give in to the temptation of tasty and high caloric food. Indeed, impulsivity has been found to predict drop out of therapy (Hjördis & Gunnar, 1989) and success of therapy (Jönnson, Björvell, Levander, & Rössner, 1986). In this latter study, several personality traits, which consitute a syndrome of ego weakness or impulsivity, predicted weight loss after 1 year. That is: the more impulsive participants lost less weight. Nederkoorn et al. (in press) found that in obese children impulsivity, measured during treatment, was related to weight loss up till that point: the more impulsive children lost less weight. Although these research findings are consistent, the support is still meagre and confirmation is needed.

In the current study, a behavioural measure of impulsivity, namely response inhibition as measured with the stop signal task (Logan, Schachar, & Tannock, 1997) was obtained from 8–12-year-old obese children before treatment. BMI was measured before and after treatment, and at 6 and 12 months follow ups. It was predicted that the most impulsive children show the least weight reduction on the different time points.