Appetite, reward sensitivity and the development of disordered eating behaviours: nature via nurture.

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Decades of twin and family studies have established that eating disorders (EDs) have a strong genetic basis, with heritability estimates in the range of 39-74% depending on the ED type. What is more, large-scale genomic studies are starting to identify specific common genetic variants involved. The environment also plays a crucial role, and it is well known that environmental factors (such as traumatic experiences, social pressures etc.) often 'trigger' the onset of ED symptoms (gene-environment interaction). However, the specific environmental factors on both EDs and ED symptoms such as binge eating are still largely unknown. Individual differences in a range of social, cognitive and behavioural traits are hypothesised to predispose to EDs, and to mediate the genetic and environmental influences on EDs. However, previous research on EDs has mainly focused on social/psychological risk factors, while behavioural traits have received far less attention. In contrast, obesity research has focused largely on behavioural traits such as appetitive traits. In particular, research from this field has established that food cue responsiveness is a key predisposing risk factor for obesity. The link between reward sensitivity and food addiction symptoms has also been of interest. However, appetitive traits and reward sensitivity as predisposing risk factors for disordered eating symptoms (such as binge-eating) have not yet been explored. A further limitation of EDs research has been the reliance on clinical samples with diagnosed EDs. Samples have tended to be small due to the low population prevalence of EDs, and focused on highly select groups who may not be representative. It is well recognised that ED symptoms exist on a continuum and population-based research into symptoms as continuous outcomes would therefore help to elucidate the aetiology of EDs. Large longitudinal studies are necessary for identifying risk factors that precede the onset of ED symptoms, but are rare.