i) Overweight/obese group: history of or current alcohol abuse or dependence, or current consumption outside recommended guidelines >21 units/week for males and >14 for females, or a score of =>8 (indicator of hazardous and harmful alcohol use) as measured using the Alcohol Use Disorder Identification Test (AUDIT); nicotine use other than "never smoked", i.e. >100 cigarettes lifetime use; history of dependence, abuse or heavy recreational use of cocaine, cannabis, opiates or other substance of abuse; history of problem gambling. Any previous or current psychiatric diagnosis listed in DSM-V Axis I, which in the opinion of the clinical team will compromise conduct and interpretability of the study.