This is the final submission of my Masters Thesis. / OBJECTIVES: Cognitive disordered eating behaviours (body shape concerns) are prevalent among youth with higher unhealthy body mass indexes (BMIs), while physical disordered eating behaviours (unhealthy changes in eating habits) are common mechanisms in determining future BMI. This thesis investigates the associations between these disordered eating behaviours and BMI categories and evaluates potential covariate modification. As a secondary objective, this thesis investigates the association between unhealthy eating patterns and BMI categories. METHODS & DATA ANALYSIS: This study was conducted among Canadian youth aged 12-17 (n=12,350). Body shape concerns were measured as the frequency of having a preoccupied desire to be thin while changing eating habits was measured as the frequency of changing eating habits to manage weight. Unhealthy eating patterns were defined as frequent restaurant eating, energy drink consumption, and skipping breakfast. Categorical BMI classifications consisted of obesity, overweight and normal/underweight. Adjusted multinomial logistic regression models were constructed. Covariates were independently tested for statistical interaction in the primary relationships. Measures of association were reported as adjusted odds ratios (ORs) with 95% confidence intervals. RESULTS: Having a preoccupied desire to be thin was associated with increased odds of being overweight and having obesity. These relationships were modified by sex, physical activity, and sleep. Changing eating habits to manage weight was associated with increased odds of being overweight and having obesity. These relationships were modified by sex. Skipping breakfast increased the odds of being overweight and having obesity, while consuming energy drinks increased the odds of having obesity. CONCLUSION: Over 40% of the sample experienced some frequency of having body shape concerns or changing eating habits to manage weight. These disordered eating behaviours increase the odds of being overweight and having obesity. Continued monitoring through national–level surveys, will be crucial in understanding changes in rates of disordered eating behaviour. / Thesis / Master of Public Health (MPH)