Dietary Patterns, Food Insecurity, and Type 2 Diabetes Risk: A Novel Platform for Population-Based Nutrition Research Using Linked Survey and Health Administrative Data in Ontario

The burden of type 2 diabetes has consistently grown in Canada over the past several decades. As current prevention efforts have been unsuccessful in curbing the diabetes epidemic, there is a need to advance our understanding of the pathways between modifiable risk factors and diabetes incidence at the population-level. Unhealthy diet has been characterized as a leading risk factor for morbidity and mortality in Canada and across peer nations over the last 20 years. Despite this observation, the majority of research considering the relationship between diet and type 2 diabetes has focused on the influence of individual nutrients as opposed to real-world patterns of dietary intake, and in the absence of considering the broader social determinants that influence these dietary patterns, such as food insecurity. At the same time, research on food insecurity rarely considers this construct beyond a descriptive marker of economic deprivation, resulting in a dearth of literature examining the diet-related chronic disease effects that stem from food insecurity. Throughout this dissertation, four studies were conducted to rigorously examine the poorly understood pathways by which modifiable dietary exposures and upstream nutrition-related social factors relate to the incidence of type 2 diabetes in the Canadian population. In doing so, a breadth of methodological approaches were applied to a unique platform for population-based nutrition research that was established through linked survey and administrative data in Ontario. The first manuscript synthesizes the published literature on dietary patterns and type 2 diabetes, as a means to understand how different methodologies can be used to comprehensively study the relationship between diet and diabetes. I found that the literature is heterogeneous with respect to viable measurement approaches for conceptualizing dietary patterns, but also gained a perspective on which approaches were the most meaningful for the Canadian context. The second manuscript investigates the prospective relationship between dietary patterns and type 2 diabetes risk for the first time in the Canadian population, improving upon many of the methodological limitations identified in studies captured in the systematic review. I found that dietary patterns most congruent with Canadian dietary recommendations were not associated with a decreased risk of type 2 diabetes, challenging findings that have persisted in the extant literature. The third study moves beyond considering the proximal relationships between diet and disease to consider the influence of food insecurity as an upstream nutrition-related social determinant of diabetes risk. I found that food insecurity is associated with a greater than 2-fold risk of type 2 diabetes over 12 years of follow-up. The fourth study extends this work to gain insight into the mechanisms by which food insecurity increases the risk of type 2 diabetes in the Canadian population. In this final study, I found that nearly 45% of the association observed in study 3 may be explained by the pathway through obesity, using sophisticated methods for causal mediation analysis. Overall this dissertation provides necessary and contemporary evidence to inform the development of population-based dietary interventions and the potential impact of social nutritional policies on the future burden of type 2 diabetes in Canada.

Keywords: causal mediation
dietary patterns
food insecurity
nutritional epidemiology
type 2 diabetes
Advisor: Rosella, Laura C