Recently, eating disorders have become the main focus of many researches, mainly due to the fact that a large number of people are affected by them. The researches are also focusing more on the biological components, or rather, changes which occur within the human body, especially the brain. Eating disorders are classified as serious mental illnesses and are characterized by an extremely low food intake as well as overeating, accompanied by a feeling of discomfort or excessive concern with weight and physical appearance. Common eating disorders include anorexia nervosa, bulimia nervosa, and binge-eating disorder. With the intent to gain new insight into the pathophysiology of eating disorders, researchers try to link cognitive processing and current nutritional behavior through studies. One way to accomplish this is to use neuropsychological tests, such as Iowa gambling task. This test was used to examine the decision-making process both in people with an eating disorder and in healthy people, and a modified version was also added to test the set shifting. Given that emotional states can affect cognitive performance and cognitive flexibility, the impact of anxiety and depression on performance was studied. The research covered the basic level of declarative knowledge and metacognition of the task, and its effect on task performance was investigated. The obtained results indicate a significantly impaired performance in subjects with an eating disorder in the original task, as well as an insignificant difference but a different pattern of performance in the modified task, compared to the control group of subjects. The results also indicate a moderate and negative effect of anxiety on the performance in block 4 and depression in block 5, while the results obtained from the control groups showed a moderate and negative effect of depression in blocks 2 and 5. Regarding the level of knowledge, the control group of subjects estimate their knowledge of the task to be significantly higher compared to the estimation of knowledge by the subjects from the clinical group. The level of declarative knowledge is significantly moderately and positively connected to the effect on performance in block 2 in the clinical group, while a moderate and positive correlation was found between metacognition and effect on performance in block 4, as well as a correlation between declarative knowledge, metacognition and relying on knowledge in block 7 among the control group of women.