Diet, nutrients, and obesity : an investigation of relationships in the Australian context

Abstract

Overweight and obesity are global public health problems affecting millions of adults, and Australia is no exception. In the population-level rise of overweight and obesity, dietary risk factors have been implicated. However, evidence is lacking on the key issues of how dietary patterns are associated with obesity outcomes: whether unhealthy diet mediates the association between socio-economic disadvantage and obesity; whether unhealthy diet is associated with weight-related complications, defined using the Edmonton Obesity Staging System (EOSS); and whether nutrient deficiencies are associated with obesity. Thus, this thesis addresses this lack, examining the relationships between diet, nutrients and obesity, and weight-related complications. In this thesis, I conducted four studies: one umbrella review and three cross-sectional studies. In the umbrella review (Study 1), I summarized and graded evidence from 16 systematic reviews of observational studies on dietary patterns and overweight/obesity outcomes in the adult population. The focus of Study 1 was the association between unhealthy versus healthy dietary patterns and overweight/obesity incidence or weight gain. For Study 2, data from 7,044 adults were analysed using log-binary regression since the prevalence of obesity in the sample was greater than 10%. To estimate the extent to which the association between socio-economic disadvantage and obesity could be explained by unhealthy diet, I also conducted mediation analysis. For Study 3, I analysed the data from 5,055 adults living with overweight or obesity and used logistic regression to explore the association between unhealthy diet and EOSS. Also, I conducted stratified analysis and propensity score matching to further examine the association in a sensitivity analysis. For Study 4, I analysed data from 3,539 adults who had biomarkers for micronutrients, applying weights to correct for the complex sampling. Results: The findings in this thesis highlight the following three points: first, diet-related efforts in obesity prevention strategies could benefit from including Mediterranean-type dietary patterns, particularly for socially disadvantaged groups. Second, since the results did not support the usefulness of the Mediterranean diet for weight-related complications, more work exploring its relationship with specific EOSS components is required. Third, the findings show the co-existence of severe obesity and vitamin D deficiency, but longitudinal studies are needed to confirm the direction of the association.

Date of Award	2022
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Evan Atlantis (Supervisor)