| Summary: | The objective of this thesis was to identify and characterise a robust phenotype susceptible to reward-driven overeating. Specifically, the thesis aimed to examine the role of liking and wanting for food in trait binge eating and to determine other potential biopsychological markers of susceptibility (psychological, physiological and genetic). In a systematic series of studies, normal-weight (Ch.6,7,9) and overweight or obese (Ch.7,8) females were categorised as either ‘binge-type’ or ‘non-binge type’ based on their scores on the Binge Eating Scale. Using a biopsychological approach, susceptibility was characterised across several different scientific domains. Liking and wanting for food were measured using the validated Leeds Food Preference Questionnaire (Ch.5-9) – LFPQ - which separated explicit and implicit processes. Food choice and energy intake were assessed objectively and quantitatively in the laboratory using ad libitum test meals (Ch.5-9) and under free-living conditions using a validated multiple-pass 24-hour dietary recall (Ch.8). Physiological markers (fat mass, fat-free mass) were measured using bioelectrical impedance and air plethysmography (Ch.6-9). Potential genetic markers of susceptibility (e.g. FTO, DRD2, Taq1A, CD36) and intermediary phenotypes of trait binge eating were examined using a candidate gene approach (Ch.9). Overweight-obese ‘binge-types’ had enhanced explicit liking for food overall, and greater implicit wanting for high-fat sweet foods compared to overweight-obese ‘non-binge types’. This was associated with an increased preference for, and consumption of these foods under laboratory and free-living conditions. Furthermore, obese ‘binge-types’ had greater levels of adiposity and reported greater food cravings and lower positive affect. Lean ‘binge-types’ had a greater implicit wanting for sweet foods, and exhibited a greater preference for these foods. Liking and wanting for food assessed by the LFPQ were related to energy intake and food choice. Notably, an enhanced liking for food in a fed state was associated with greater energy intake. In addition, implicit wanting emerged as an important process; while enhanced implicit wanting for sweet foods was a risk factor for overeating, greater implicit wanting for low-fat savoury foods appeared to be protective. Examination of the intermediary phenotypes revealed that variation in certain genes relating to reward, taste and obesity were associated with energy intake and food choice, body composition and food hedonics. This thesis has identified a distinct, ecologically valid, behavioural phenotype of obesity that is characterised by reliable psychological and physiological characteristics. Furthermore, the results confirm the value of distinguishing between liking and wanting for food and for studying their role in eating behaviour.
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