Computational mechanisms underpinning greater exploratory behaviour in excess weight relative to healthy weight adolescents.

Obesity in adolescence is associated with cognitive changes that lead to difficulties in shifting unhealthy habits in favour of alternative healthy behaviours, similar to addictive behaviours. An outstanding question is whether this shift in goal-directed behaviour is driven by over-exploitation or over-exploration of rewarding outcomes. Here, we addressed this question by comparing explore/exploit behaviour on the Iowa Gambling Task in 43 adolescents with excess weight against 38 adolescents with healthy weight. We computationally modelled both exploitation behaviour (e.g., reinforcement sensitivity and inverse decay parameters), and explorative behaviour (e.g., maximum directed exploration value). We found that overall, adolescents with excess weight displayed more behavioural exploration than their healthy-weight counterparts - specifically, demonstrating greater overall switching behaviour. Computational models revealed that this behaviour was driven by a higher maximum directed exploration value in the excess-weight group (U = 520.00, p = .005, BF10 = 5.11). Importantly, however, we found substantial evidence that groups did not differ in reinforcement sensitivity (U = 867.00, p = .641, BF10 = 0.30). Overall, our study demonstrates a preference for exploratory behaviour in adolescents with excess weight, independent of sensitivity to reward. This pattern could potentially underpin an intrinsic desire to explore energy-dense unhealthy foods - an as-yet untapped mechanism that could be targeted in future treatments of obesity in adolescents.

Bioelectrical impedance analysis to estimate body composition, and change in adiposity, in overweight and obese adolescents: comparison with dual-energy x-ray absorptiometry.

BACKGROUND: There is a need for a practical, inexpensive method to assess body composition in obese adolescents. This study aimed to 1) compare body composition parameters estimated by a stand-on, multi-frequency bioelectrical impendence (BIA) device, using a) the manufacturers' equations, and b) published and derived equations with body composition measured by dual-energy x-ray absorptiometry (DXA) and 2) assess percentage body fat (%BF) change after a weight loss intervention. METHODS: Participants were 66 obese adolescents, mean age (SD) 12.9 (2.0) years. Body composition was measured by Tanita BIA MC-180MA (Tanita BIA8) and DXA (GE-Lunar Prodigy). BIA resistance and reactance data at frequencies of 5, 50, 250 and 500 kHz, were used in published equations, and to generate a new prediction equation for fat-free mass (FFM) using a split-sample method. Approximately half (n = 34) of the adolescents had their body composition measured by DXA and BIA on two occasions, three to nine months apart. RESULTS: The correlations between FFM (kg), fat mass (kg) and %BF measured by BIA and DXA were 0.92, 0.93 and 0.78, respectively. The Tanita BIA8 manufacturers equations significantly (P < 0.001) overestimated FFM (4.3 kg [-5.3 to 13.9]) and underestimated %BF (-5.0% [-15 to 5.0]) compared to DXA. The mean differences between BIA derived equations and DXA measured body composition parameters were small (0.4 to 2.1%), not significant, but had large limits of agreements (~ ±15% for FFM). After the intervention mean %BF loss was similar by both methods (~1.5%), but with wide limits of agreement. CONCLUSION: The Tanita BIA8 could be a valuable clinical tool to measure body composition at the group level, but is inaccurate for the individual obese adolescent.

Effect of a prescriptive dietary intervention on psychological dimensions of eating behavior in obese adolescents.

BACKGROUND: Overweight adolescents are more likely to have dysfunctional eating behaviours compared to normal weight adolescents. Little is known about the effects of obesity treatment on the psychological dimensions of eating behavior in this population. OBJECTIVE: To examine the effects of a prescriptive dietary intervention on external eating (eating in response to food cues, regardless of hunger and satiety), emotional eating and dietary restraint and their relation to weight loss. Parental acceptability was also examined. METHOD: This is a secondary study of a 12-month randomized trial, the RESIST study, which examined the effects of two diets on insulin sensitivity. Participants were 109 obese 10- to 17-year-olds with clinical features of insulin resistance. The program commenced with a 3-month dietary intervention using a structured meal plan, with the addition of an exercise intervention in the next 3 months and followed by a 6 month maintenance period.This paper presents changes in eating behaviors measured by the Eating Pattern Inventory for Children and parent rated diet acceptability during the first 6 months of the trial. As there was no difference between the diets on outcome of interest, both diet groups were combined for analyses. RESULTS: After 6 months, the proportion of participants who reported consuming more in response to external eating cues decreased from 17% to 5% (P = 0.003), whereas non- emotional eating increased from 48% to 65% (p = 0.014). Dietary restraint and parental pressure to eat remained unchanged. A reduction in external eating (rho = 0.36, P < 0.001) and a reduction in dietary restraint (r = 0.26, P = 0.013) were associated with greater weight loss at 3 and 6 months, respectively. Overall this approach was well accepted by parents with 72% of parents considered that their child would be able to follow the meal plan for the longer term. CONCLUSIONS: In the short to medium term, a prescriptive dietary intervention approach is a well-accepted and suitable option for obese adolescents with clinical features of insulin resistance. It may reduce external and emotional eating, led to modest weight loss and did not cause any adverse effect on dietary restraint. TRIAL REGISTRATION: Australian New Zealand Clinical Trial Registration Number (ACTRN) 12608000416392 https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=83071.

Dietary glycemic load, insulin load, and weight loss in obese, insulin resistant adolescents: RESIST study.

BACKGROUND & AIMS: The optimal dietary approach for weight loss and improving insulin sensitivity in adolescents is unknown. This study aimed to explore the association between the estimated insulin demand of the diet, as measured by glycemic and insulin load, weight loss, percentage body fat and insulin sensitivity index (ISI) in obese adolescents with clinical features of insulin resistance and/or prediabetes after a 3 month lifestyle and metformin intervention. METHODS: Secondary data analysis of 91 adolescents (median age 12.7 years (range 10.1-17.4) participating in a randomized controlled trial, known as RESIST; ACTRN12608000416392. Weight change between baseline and 3 months was measured by BMI expressed as percentage of the 95th centile (BMI %95). Body composition was measured by dual energy X-ray absorptiometry and ISI was determined by an oral glucose tolerance test. RESULTS: Higher dietary glycemic load and insulin load were associated with less weight loss (BMI %95), adjusted for sex and pubertal stage, ß = 0.0466, P = 0.007 and ß = 0.0124, P = 0.040, respectively. Inclusion of total energy intake in the model explained observed associations between dietary glycemic load and insulin load and change in BMI %95. Neither dietary glycemic load nor insulin load were associated with changes in percentage body fat or ISI. Dietary glycemic index and macronutrient content (% of total energy) were not associated to changes in BMI %95, percentage body fat or ISI. CONCLUSION: Reduced energy diet contributes to weight loss in obese, insulin resistant adolescents. Diets with a lower insulin demand were associated with a lower energy intake and may hence assist with weight loss.

Vitamin B12 in obese adolescents with clinical features of insulin resistance.

Emerging evidence indicates an association between obesity, metformin use and reduced vitamin B12 status, which can have serious hematologic, neurologic and psychiatric consequences. This study aimed to examine B12 status in obese adolescents with pre-diabetes and/or clinical features of insulin resistance. Serum B12 was measured using chemiluminescence immunoassay in 103 (43 male, 60 female) obese (mean body mass index (BMI) z-score ± SD (2.36 ± 0.29)), adolescents aged 10 to 17 years, median (range) insulin sensitivity index of 1.27 (0.27 to 3.38) and 13.6% had pre-diabetes. Low B12 (<148 pmol/L) was identified in eight (7.8%) and borderline status (148 to 221 pmol/L) in an additional 25 (24.3%) adolescents. Adolescents with borderline B12 concentrations had higher BMI z-scores compared to those with normal concentrations (2.50 ± 0.22 vs. 2.32 ± 0.30, p = 0.008) or those with low B12 concentration (2.50 ± 0.22 vs. 2.27 ± 0.226, p = 0.041). In conclusion, nearly a third of obese adolescents with clinical insulin resistance had a low or borderline serum B12 status. Therefore, further investigations are warranted to explore the cause and the impact of low B12 status in obese pediatric populations.

Optimal macronutrient content of the diet for adolescents with prediabetes; RESIST a randomised control trial.

CONTEXT: Prediabetes and clinical insulin resistance in adolescents are rapidly emerging clinical problems with serious health outcomes. OBJECTIVE: The objective of this study was to determine the efficacy of 2 structured lifestyle interventions, both differing in diet macronutrient composition, on insulin sensitivity. DESIGN: This study was a randomized controlled trial, known as Researching Effective Strategies to Improve Insulin Sensitivity in Children and Teenagers, in 2 hospitals in Sydney, Australia. PARTICIPANTS: Participants included overweight or obese 10- to 17-year-olds with either prediabetes and/or clinical features of insulin resistance. INTERVENTION: At baseline adolescents were prescribed metformin and randomized to a structured diet, which was either high carbohydrate or moderate carbohydrate with increased protein. The program commenced with a 3-month dietary intervention, with the addition of an exercise intervention in the next 3 months. OUTCOMES: The outcomes included an insulin sensitivity, anthropometry, and cardiometabolic profile at 6 months. RESULTS: One hundred eleven subjects (66 girls) were recruited and 98 subjects (58 girls) completed the 6-month intervention. After 3 months the mean insulin sensitivity index increased by 0.3 [95% confidence interval (CI) 0.2-0.4]. After 6 months the mean insulin (picomoles per liter) to glucose ratio (millimoles per liter) decreased by 7.2 [95%CI -12.0 to -2.3], body mass index, expressed as a percentage of the 95th centile, decreased by 9% (95% CI -3 to -15), but there was no significant change in the lipids. There were no significant differences in outcomes between the diet groups at any time point. CONCLUSIONS: These results are in contrast with our hypothesis that adolescents randomized to the increased protein diet would have better outcomes. Further strategies are required to better address prediabetes and clinical features of insulin resistance in adolescents.