Inhibitory control and perception of the future health in obese adolescents and normal weight adolescents

Abstract

BackgroundChildhood obesity tracks into adulthood, meaning obesogenic behaviours learned in early years are likely to be sustained throughout life. Studies of the neurocognitive mechanisms underlying obesity-related behaviours have implicated the role of impulsivity in weight gain. Food-related and physical-activity-related impulsive actions such as discounting of the future health benefits of present rewards or the inability to inhibit tempting unhealthy choices can lead to gradual weight gain. Impulsivity was compared in a group of obese and non-obese adolescents to test this hypothesis. Methods47 obese adolescents (mean body-mass index [BMI] 33·22 [SD 8·0]) who attended a residential lifestyle summer camp with a mean age of 14·28 years (SD 1·7) were recruited with parental consent over two summers. A normal weight control group (BMI 20·6 [SD 2·3]) with a mean age of 13·83 years (SD 1·7) from a UK secondary school were used for comparison. Behavioural measures of impulsivity were tested using the stop signal reaction time (SSRT) as a marker of inhibitory control and the temporal discounting constant for monetary rewards. Self-reported scores of impulsivity using Cloninger's junior temperament and character inventory were correlated with behavioural measures by use of a Spearman's correlation. FindingsThe non-obese group had better inhibitory control as measured by the SSRT with a mean value of 156·93 ms (SD 43·12) compared with the obese group with a mean value of 218·42 ms (80·48; p=0·0001). Additionally, SSRT direction errors were significantly higher in the obese adolescents (5·48 [SD 4·88]) than in normal weight individuals (2·88 [0·41]; p=0·0001), and the proportion of successful stops were significantly higher in the normal weight adolescents (0·49 [SD 0·1]) than in the obese group (0·53 [0·09]; p=0·02). Those who were obese (k=0·56 [SD 0·36]) were found to discount the future value of money significantly more than normal weight individuals (0·40 [0·29]; p=0·018) and scored higher on the novelty seeking subscale of the junior temperament and character inventory (r=0·23; p=0·03). InterpretationImpulsivity is a unitary construct, which is an independent predictor of BMI in adults and may act as a causal factor in adolescents. Obese adolescents exhibit poor inhibitory control and discount the future for monetary rewards more than their non-obese counterparts. In addition, there were greater response errors and a failure to stop during the no-go paradigm, suggesting the presence of either inattention or hyperactive traits in addition to impulsive behaviours in the obese group. The difference in socioeconomic status between both groups may be a confounding factor and was not available for analysis. Bias was reduced by ensuring all participants were in full-time education, matched for age, and masked to testing. Understanding of the neurocognitive mechanisms underlining obesogenic behaviours such as impulsivity is needed to improve existing interventions, through the development of novel methods to train self-control and self-efficacy as part of a personalised approach to weight reduction. FundingNone.