The neurobiology of eating behaviour: an investigation into the construct of food addiction in young Australian adults

Research Doctorate - Doctor of Philosophy (PhD)The concept of “food addiction” generates a considerable amount of interest and debate in both the media and the scientific arenas. Numerous behavioural and neurobiological parallels have been identified between specific eating behaviours and substance dependence, such as drug and alcohol addiction. However, the majority of supporting evidence for the phenomenon is derived from animal models, with limited and inconsistent findings in humans. This thesis aimed to explore the construct of food addiction in the young Australian adult population in relation to dietary intake profiles and activation of brain reward networks to visual food cues. To investigate this aim, this thesis presents a series of four related studies, which were informed by two systematic reviews. Two systematic reviews of the literature were conducted to evaluate current evidence with respect to: (i) neural responses to visual food cues, as assessed by functional magnetic resonance imaging (fMRI). ; (ii) studies that have used the Yale Food Addiction Scale (YFAS), a tool specifically designed to evaluate addictive-like eating behaviours in adults. The first of these reviews identified that obese individuals displayed increased reward-related neural activation to visual food cues compared to individuals of a normal body weight. This review also highlighted that standardisation of study conditions and outcome reporting is imperative in studies of this nature, in order to facilitate more direct comparisons across studies. The second review found the weighted mean prevalence of food addiction to be 19.9% across published studies using the YFAS to 2014, and that food addiction prevalence was higher in population samples of females, overweight/obese individuals and individuals with clinically diagnosed disordered eating. This review identified a number of key gaps in the YFAS evidence base, including the paucity of studies investigating specific foods and neural correlates associated with YFAS assessed food addiction, as well as community-based studies evaluating the food addiction construct at multiple time points. The limitations identified in these reviews were addressed in the subsequent thesis studies. An online cross-sectional survey was conducted to explore the foods associated with YFAS assessed food addiction in young adults. The survey included demographics, anthropometrics, YFAS and the Australian Eating Survey (AES), a validated dietary intake assessment tool. A total of 462 predominantly female, normal weight participants completed the survey, with 14.7% (n= 68) classified as food addicted. Higher YFAS symptom scores were associated with having a higher percentage energy intake (%E) from energy-dense, nutrient-poor foods, including confectionary, take-away foods and baked sweet products such as cakes and pastries. Higher symptom scores were also associated with a lower %E from nutrient-dense core foods, including whole-grain products and breakfast cereals. This was the first study to characterise the foods associated with YFAS assessed food addiction, and requires replication in a nationally representative population sample. A validation study was conducted to evaluate the accuracy of online self-reported anthropometrics in young adults, given that weight and body mass index (BMI) could be associated with food addiction. In order to conduct online food addiction surveys, this was important to establish. Young adults reported their current height and weight as part of an online survey, and had the same data objectively measured. Measured and self-reported data were strongly positively correlated and had fairly good agreement. Self-reported height was overestimated, while self-reported weight and calculated BMI were underestimated. However, these discrepancies were small (