Weight loss in adolescents: Measuring benefits and outcomes

Kimberley Baxter (2011). Weight loss in adolescents: Measuring benefits and outcomes PhD Thesis, School of Medicine, The University of Queensland.

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Author Kimberley Baxter
Thesis Title Weight loss in adolescents: Measuring benefits and outcomes
School, Centre or Institute School of Medicine
Institution The University of Queensland
Publication date 2011-12
Thesis type PhD Thesis
Supervisor Professor Helen Truby
Professor Jennifer Batch
Dr James Sharman
Dr John Cardinal
Total pages 303
Total colour pages 18
Total black and white pages 285
Language eng
Subjects 1111 Nutrition and Dietetics
Abstract/Summary One in five Queensland children are overweight or obese; however the lack of weight management services remains a major barrier to families seeking assistance. Evidence indicates that childhood obesity is resistant to treatment and tends to track into adulthood, bringing with it the associated risk of chronic disease. There is a need for effective treatment pathways, particularly for adolescents with severe obesity. Dietetics provides the opportunity to impact on childhood obesity but traditionally has relied on standard advice based on unstructured low fat eating. Evidence in adults suggests that a reduction in dietary carbohydrate could provide an alternative dietary pattern. A 12 week pilot study (n=30 participants, mean age 13 years, mean body mass index (BMI) z-score 2.2) investigated the feasibility and acceptability of a structured reduced carbohydrate dietary plan (energy distribution: fat 35%: protein 30%: carbohydrate 35%) and a structured low fat dietary plan (25% fat: protein 20%: carbohydrate 55%) compared with ‘standard care’ (an unstructured low fat approach). Participants self-selected which dietary program they commenced and attended 6 nutrition counselling appointments. Only two individuals chose the ‘standard care’ option, 13 chose the structured low fat option and 15 chose to modify their carbohydrate intake. Participants indicated a strong preference for structured dietary advice. This pilot study highlighted that food records had high levels of implausible energy intakes (53% of participants) but macronutrient distribution appeared to be unaffected by under-reporting and was a useful method to gauge dietary compliance. Participants were very sedentary and were unable to alter their physical activity; had a range of biochemical abnormalities and had evidence of psychosocial issues including school absence. Mean BMI z-score loss was -0.20 in the structured low fat group, -0.11 in the reduced carb group and those choosing ‘standard care’ gained weight (+3.1kg) over the 12 week period (mean BMI z-score change -0.02). The outcomes demonstrated that the referral pathways were successful and that families had a preference for a structured eating plan approach. A 12 week randomised controlled trial entitled the ‘Eat Smart’ study was conducted with the primary aim to evaluate the relative efficacy of a structured low fat versus a structured reduced carbohydrate eating plan versus a control group; the primary outcome measure was BMI z-score. A psychological preparedness group program provided a preliminary step to ensure that all subjects entering the dietary phase were psychologically stable and ready for change. Of 87 individuals (mean age 13.3 years, 79% female) randomised, 79 completed (90.8%) the 12 week intervention period. At week 12 there was a significant overall association between diet and BMI z-score (p<0.001); with post-hoc analyses indicating significant differences between the active diets and the control group. There was no difference between the modified carbohydrate (mean reduction in BMI z-score of -0.13) and low fat group (mean reduction in BMI z-score of -0.12). There were no significant differences between the modified carbohydrate and low fat groups for secondary outcome measures except ICAM-1 (p=0.02). To confirm that there was no detectable dietary effect on change in anthropometric and biochemical outcomes a between group analysis was conducted of all outcome variables (anthropometric and biochemical). Analysis confirmed that there was no difference for any change variables between the low fat and modified carbohydrate groups. Pubertal compared with pre-pubertal status (with BMI z-score as a covariate) did not influence biochemical markers of insulin resistance, cytokines or adipokines at baseline. Gender was investigated with both puberty and BMI z-score as covariates, and found to affect leptin (p-value = 0.001) with girls appearing to have significantly higher levels than their male peers. To investigate the impact of weight change on specific cardiovascular risk factors, a completers dataset from the pilot and the RCT was constructed (n=100). Participants were grouped as responders (≥5% BMI z-score change) and non-responders (<5% BMI z-score change). Key within group differences were evident at week 12 in the responders, including: weight, BMI z-score, insulin, HOMA-IR, total cholesterol, ALP, AST, GGT, adiponectin, leptin, IL-6, TNF-α and blood pressure. To explore treatment response; univariate regression modelling determined which characteristics (physiological and psychosocial) could be useful in explaining the variance in reduction in BMI z-score. The primary baseline factors identified (R2 =36%) were lower BMI z-score, lower insulin resistance (HOMA-IR), higher social advantage (SEIFA) and referral from a specialist. Overall this research has demonstrated that modifying dietary carbohydrate is equivalent to a low fat approach in the short term in regards to weight loss and has no adverse effect on biochemical factors. Weight loss itself, rather than diet type appeared to be the driving factor in reducing cardiometabolic risk, with favourable changes evident even with modest reductions in BMI z-score. The BMI z-score outcomes achieved in the Eat Smart study were comparable with the mean effect size published in the 2009 Cochrane review suggesting that this protocol has applicability in the clinical setting. These results also demonstrate that early intervention for those with lower BMI z-scores was associated with greater likelihood of treatment success. Longer term follow up studies of adolescents who successfully reduce and maintain lost weight are required to determine if such an intervention may lead to a clinical benefit in regard to reduction in chronic disease mortality and morbidity.
Keyword obesity
Predictors of treatment outcome
Inflammatory Markers
Weight loss programs
Dietary intervention
Additional Notes colour pages: 52, 84, 87, 91, 97, 99, 100, 114, 121, 124, 135, 139, 141, 143, 162, 175, 176, 188 landscape: 142, 145, 275, 276, 277, 279, 280, 282, 283, 284, 301

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Created: Wed, 27 Jun 2012, 16:06:27 EST by Kimberley Baxter on behalf of Library - Information Access Service