Research Doctorate - Doctor of Philosophy (PhD) / The prevalence of overweight and obesity in Australian children continues to rise. Without receiving treatment, many of these children will become overweight or obese adults and will develop a range of associated health problems and incur higher direct and indirect health costs compared to those who remain healthy weight. There is marked disparity between the scale of the public health issue and the evidence on how to best treat childhood obesity and which elements of dietary interventions are effective. Reviews of previous treatment studies have acknowledged methodological weaknesses which need to be addressed. Descriptions of dietary interventions, dietary intake and changes in dietary intake of children are rarely reported. This may be partly due to the lack of validated assessment tools available for use with paediatric populations. There is no question of the importance of diet in helping to reduce child obesity levels; the role of dietary treatment alone is difficult to elucidate. Consequently it is unknown what comprises an effective dietary treatment as studies to date have produced modest results and there is an ongoing need to identify which factors could improve weight related outcomes. The first aim of the studies in this thesis was to validate parental reports of young children’s fruit and vegetable intake using a child specific Australian food frequency questionnaire (FFQ) and comparing reported intakes with nutritional biomarkers. The second aim was to comprehensively describe a dietary intervention treatment program for use in a methodologically high quality obesity treatment randomised controlled trial (RCT). Thirdly, this thesis aimed to describe the parental reports of the child participants’ dietary intakes and food behaviours using the FFQ and report the parent child feeding practices. These outcome measures are reported both in the short-term (post-intervention) and the long-term (12 months post-intervention). The underlying hypothesis was that the group receiving the dietary intervention would achieve better dietary outcomes compared with a group given a physical activity treatment program only. An additional aim of the thesis was to investigate the feasibility of developing a brief dietary intake assessment tool for use in clinical and community settings by undertakinga feasibility study on the development of a diet variety score for use in assessing children’s dietary intakes. Results from the validation study of a child specific FFQ against objective nutritional biomarkers in study 1 (Chapter 3) showed that there was a moderately strong relationship between parent reported intakes of fruit and vegetables using the Australian Schools Eating Survey (ASES) FFQ with fasting plasma carotenoids. This was after adjustment for child body weight. The ASES FFQ was a useful tool for estimating the dietary intakes of fruit and vegetables in younger children via parental report. A comparative study (Chapter 4) between overweight and obese children recruited to an obesity treatment intervention and a community sample illustrated that all parents’ over-report children’s dietary intakes of foods consumed when using the ASES FFQ. Relative dietary differences were detected between the groups for the percentage energy derived from the non-core extras food group of The Australian Guide to Healthy Eating. Parents of overweight children reported more controlling methods of child feeding The detailed description of the dietary intervention used in the RCT will allow for the possibility of replication of the key elements of this approach in child obesity treatment programs. The detailed reported changes in dietary intakes resulting from the obesity treatment intervention (Chapter 5), both in the short and long-term, demonstrated that all treatment groups were effective in improving children’s dietary intakes and in reducing total energy intakes, up to one year. The comprehensive reports have facilitated the identification of effective components of dietary interventions and identified foods, lifestyle behaviours that are able to be modified and sustained by families of overweight children. In addition, it was shown that a parent’s child feeding practices can be changed and sustained secondary to an obesity treatment program. While parent child feeding practices require further investigation, this could contribute to improving the outcomes of future studies. The dietary score feasibility study (Chapter 6), found that a dietary variety score, based on the ASES FFQ was a feasible option for reporting on children’s dietary intake more universally as an indicator of whole food consumption, rather than nutrient intake. However, the score was not directly useful in the current study and the diet variety scorehas methodological weaknesses that need to be addressed before it can be used as intended. In conclusion, the findings reported in this thesis have shown the ASES FFQ is a useful tool for estimating younger children’s fruit and vegetable intake via parental report. All treatment arms of the HIKCUPS RCT were equally efficacious in improving children’s dietary intakes. This study gives unique insights to the effectiveness of a specific dietary intervention and adds to the evidence base for targeting decreases in total energy, fat, sugar, sweetened drinks and take-away foods, increasing the consumption of low fat dairy products and vegetables. It also supports using parents as the agent of lifestyle change. Furthermore, it was shown that specific child feeding domains are modifiable in the context of a targeted obesity intervention which highlights the importance of addressing broader parenting issues in the management of childhood overweight and obesity. This thesis has several novel aspects: it reports a comparative validation study of a contemporary Australian FFQ; it provides a detailed description of a dietary intervention used in the treatment of childhood obesity and the resultant dietary changes after an obesity intervention and changes to the child feeding practices of parents of obese children.