Fasting constitutes a foundational discipline within Christian spiritual life. Its roots lie in Jewish practice, which included designated fast days. The Gospels attest that Christ himself undertook a forty-day fast in the desert, and the example of St. John the Baptist—who lived on locusts and wild honey—became paradigmatic for later tradition. Hagiographic sources consistently underscore the importance of fasting in the lives of the saints. The Vita of St. Nicholas relates that he refused his mother's milk on Wednesdays and Fridays, a motif repeated in the Life of St. Sergius of Radonezh. Monastic asceticism presupposed a reduced diet—according to John Cassian, mainly bread and vegetables, with fish as a rare allowance. Yet the vitae of monks and hermits often describe even stricter abstinence. St. Macarius the Great is said to have eaten only once a week during Great Lent, while St. Theodosius of the Caves spent the entire Lenten period in seclusion. In the East Slavic tradition, fasting became a defining mark of sanctity: St. Sergius of Radonezh is described as living on bread and water and abstaining from food on Wednesdays and Fridays, and St. Euthymius of Suzdal was called the "co-faster of Sergius." Over time, hagiographers emphasized not only minimal food intake but also the theological meaning of fasting as repentance and inner purification. In the twentieth century, fasting вновь became a subject of theological reflection. The Church Fathers had long taught that fasting, especially during Great Lent, serves primarily for the purification of the soul. This view was echoed by the Russian priest Alexander Men, who stressed its spiritual focus. In the twenty-first century, interest in fasting has grown, though discussions often center on dietary rules. Despite this attention, participation remains limited: in 2024 only 17% of Russians intended to keep the full fast, while 37% planned partial restrictions.