During the Late Middle Ages, the practice of fasting among religious women in an attempt to follow a pious and ascetic life was common. In this paper, three cases of medieval religious women are described with a particular attention to the figure of St. Catherine of Siena, her life, popularity, and iconography. In the Middle Ages, holy fasting was characterized by a refusal to eat that could involve binging and purging, lack of menstruation, an interest in cooking for others, and in some cases death due to inanition. In the Medieval narratives of fasting holy women, we can see patterns that are compatible with symptoms of anorexia nervosa. From a psychiatric perspective, it is possible to elucidate and understand the practice of fasting among religious people in the Late Middle Ages.