Background—The nutritional status of women and children continues to be a global public health concern, particularly in low- and middle-income countries. While improvements have been gained in nutrition-related health indicators In Ethiopia, 38% of children under five remain stunted, 25% of women of reproductive age are undernourished, and an estimated 1.7 million children, pregnant, and breastfeeding women require specialised nutrition support. Maternal dietary and child nutrition is not solely the result of access to food. Orthodox Christianity is practised by an estimated 40 million people in Ethiopia and strictly prohibits the consumption of animal products and restricts the times allowed for eating for the 200 days per year that are designated fasting days; yet, there is little understanding of its practice amongst pregnant and breastfeeding women. Research Aim—To increase our understanding of how and why Ethiopian Orthodox women practice religious fasting during pregnancy and when breastfeeding through their own accounts. Methods— Using a social ecological framework, interviews with pregnant and breastfeeding women explored the interrelated factors that contribute to dietary behaviour during these nutritionally important periods, including social norms and religious decisions around fasting. A sample of 19 participants was selected purposively for interviews from both urban and rural sites in the Amhara Region of Ethiopia. Interviews were conducted in the local language, audio recorded. Using NVivo software, transcribed interviewed were analysed to define thematic areas. Results—Religiosity and its effect on health was a major theme of women’s nutrition experiences which drove their motivation and behaviour, intersecting all other themes and subthemes. There was a closely linked association between women’s experiences of the physical effects of pregnancy, breastfeeding during fasting and the spiritual experience of fasting. Women’s exercise of agency in their fasting behaviour and their conception of health as encompassing both spiritual and physical aspects were identified as major themes. The influence of social networks, including peer, family, and community, also played an important role in women’s dietary choices during pregnancy and breastfeeding. Conclusion—Recognizing spiritual well-being as a normative health framework for Ethiopian Orthodox women may in fact facilitate adoption of the types of multisectoral approaches to undernutrition that are recommended in global health nutrition guidance. Directly involving priests and lay community members as more prominent stakeholders to address undernutrition in this socio-cultural context may result in more effective strategies to reduce nutrition-related maternal and child morbidities and mortality in Ethiopia.