Part 1: This thesis begins with a literature review of the evidence base of the neuropsychological profile of adolescents with anorexia nervosa (AN). A systemic review identified 36 relevant studies. Results indicated inconsistent findings across studies throughout each neuropsychological domain under review, such as some finding set-shifting difficulties in some young people with AN while others did not find any differences in performance. Adolescents with AN typically performed within the average range, with many studies not finding any significant differences between their performance and healthy adolescents' performance. Performance often improved following weight-gain. Drawing firm conclusions about these findings was hampered by methodological and task differences between the studies. Future research should endeavour to take into account the potential impact of confounding variables, such as co-morbid diagnoses and psychoactive medication, on outcome measures in this population. / Part 2: The empirical paper reports the results of a joint study that investigated the effects of intermittent fasting in healthy adults, using the 5:2 diet. This within-subjects study explored the differences in performance on fasting versus non-fasting days, on a series of cognitive tasks. The results indicated no significant differences between fasting and non-fasting days on any task administered. This suggests there are no detectable effects of the 5:2 diet on the cognitive domains assessed over a brief time period. These findings do not replicate the results found in acute fasting studies, but are more in line with those reported from other dieting strategies. / Part 3: Finally, the critical appraisal offers some reflections on the whole research process. It emphasises the need for different methodologies to tackle the complex problem of understanding and treating eating disorders. It also considers the benefits of the scientist-practitioner model.