Emotional overeating (EOE) and under-eating (EUE) in response to stress are common behaviours which emerge in childhood. However, their aetiology is largely unknown. This thesis analysed data from a UK cohort of 2402 families with twins to investigate the aetiology of EOE and EUE in childhood. Study 1 demonstrated low heritability of EOE at 16 months (9%) and five years (3%). The majority of individual differences were explained by shared environmental factors (16 months: 89%, 5 years: 95%). However, only 8% of these environmental factors were found to influence EOE at both time points. EOE was found to track (r = 0.25) and this association was explained by shared environmental factors. Study 2 established low heritability (7%) for EUE and dominance of shared environmental factors (91%) at five years. EOE and EUE correlated (r = 0.43) and shared environmental factors accounted for this association. However, their aetiologies were partly distinct, with 25% of shared environmental factors affecting both behaviours. Study 3 characterised the child, parent and environmental factors associated with child EOE and EUE. Emotional feeding was found to influence both EOE and EUE, whereas parental pressure to eat was only associated with EUE. Maternal emotional overeating was specifically linked to EOE. Study 4 provided evidence for the causal effect of emotional feeding on child EOE using prospective data. Study 5 found significant gene-environment interactions underlying EOE and EUE whereby a stressful home environment increased their heritability. Study 6 replicated Study 2 in an independent sample. Study 7 showed that parental belief of twins’ zygosity did not impact their ratings of child eating behaviours. The thesis showed that EOE and EUE are learned and not inherited in childhood. Their aetiology is complex and due to specific parental behaviours which deem to be promising intervention targets
