Advances in geochemical and physical anthropological studies have provided new tools to reconstruct ancient lifestyles, especially of those minorities not commonly mentioned in historical texts. In comparison to males, little is known about everyday life in female monastic communities, and how it has changed over time. In this paper, we present a paleodietary (δ 13 C and δ 15 N in bone collagen) study of human (n = 58) and animal (n = 13) remains recovered from the former Convent of Santa Catalina de Siena in Belmonte (Cuenca, central Spain). Two funerary areas used by Dominican nuns were sampled: one dated to the sixteenth (n = 34) and the seventeenth (n = 15) centuries, and the other dated in the nineteenth and twentieth (n = 9) centuries. The isotopic values for sheep (n = 7) suggest the animals consumed at the convent came from diverse ecosystems or were raised under a range of management strategies. The human samples reflect a terrestrial diet, and those from the nineteenth to twentieth century, in some cases, reveal the presence of C 4 plants (millet, corn or sugar cane). Due to their religious practice, the consumption of terrestrial animal protein was restricted, and although they were allowed to eat fish, the isotopic signatures show little evidence of this. The individuals from the sixteenth and seventeenth century show a continuous shift in δ 15 N (9.7-12.7‰), with few significant differences in relation to the period, age, or pathologies (osteoporosis, periostitis, and brucellosis). The nineteenth-to twentieth-century samples can be divided into two groups: (a) one that fits the trend of previous centuries, albeit with a higher δ 15 N, possibly related to extensive access to animal protein; and (b) a second group with elevated δ 13 C values (up to − 15.7‰). Different customs in the assumed homogeneous monastic life are discussed as possible sources of isotopic variation, including access to luxury products such as animal protein or sugar, or the practice of periods of food abstinence, which were especially popular with these communities, according to historical records.