Anorexia nervosa (AN) is known as the psychiatric disorder with the highest mortality rate as long-term calorie restriction causes medical complications and suicide risk. The ineffectiveness of pharmacological treatments increases interest in the etiopathogenesis of the disease. This study aims to examine the effects of caloric and non-caloric food intake on stress response, changes in brain network activity in AN patients and healthy volunteers, and examine whether these changes are related to caloric intake through neuroendocrine and psychological responses. The study will include 30 female AN patients aged 13-18 who are newly diagnosed and have not received any treatment, and 30 healthy volunteers matched by age, sex, and education level. The patient group will be admitted to the clinic's open inpatient unit on the evening before the study to ensure they have fasted. A 12-hour fasting period starting from the day before the procedure will be mandatory. In the morning, patients will undergo psychiatric assessments and scales. Psychometric measurements will be applied to determine the clinical characteristics of participants. Visual Analog Scale (VAS) will be applied. VAS is used to evaluate subjective states such as hunger, satiety, desire to eat, anxiety, fear of obesity, sadness, appetite, general mood, and motivation to participate in the study. Following this, the first resting-state functional magnetic resonance imaging (fMRI) scan will be performed for 8 minutes. Subsequently, participants will be randomised with 1:1 allocation ratio to consume one of two jellies prepared by a dietitian: one containing 400 calories and the other calorie-free. Participants will not be forced to consume the food. The ingredients and preparation methods were chosen to make the appearance and taste of the foods similar. Participants will not know which type of food (caloric/non-caloric) they are given. Participants who do not wish to consume the provided food will be excluded from the study. Participants will be told that the mixture they will be consuming will either be balanced in nutritional value and caloric, or harmless and calorie-free. They will be given fifteen minutes to consume the mixture, and the amount they consume will be recorded. Sixty minutes after the consumption of the mixture, participants will undergo a second fMRI scan to identify the neuronal network changes induced by this process. The same procedures will be applied to the healthy control group. Before and after imaging, blood samples will be collected from participants for biochemical analysis. Endocrine markers such as glucose, insulin, ghrelin, obestatin, PYY, leptin, and cortisol will be evaluated to assess hunger, satiety, and stress responses. Changes in these parameters will be used to evaluate participants' physiological responses to meals. A second meal will be offered three hours after the first meal, and the amount consumed will be recorded. Four subgroups will be analysed in the study: AN patients who received calories, AN patients who did not receive calories, healthy controls who received calories, and healthy controls who did not receive calories. Outcome data will be collected before and after meal intake and the outcomes will be compared between the four groups. The study aims to investigate the physiological, psychological and behavioural responses to caloric and non-caloric meals, and to compare the responses in patients and non-patients. It is hypothesized that the stress response observed in AN patients is not solely related to food intake but that the calorie content of the ingested food will cause additional activation in biologically stress-related networks, with corresponding effects on experience. The hypothesis that the differences observed between patients and controls are due to biological differences in AN patients will be tested. This study aims to shed light on the etiopathogenesis of AN and contribute to the development of new strategies for the treatment and management of AN.