In Ethiopia, children and adults face a double burden of malnutrition, with undernutrition and stunting coexisting with non-communicable diseases. Here we use a framework of comparative risk assessment, local dietary surveys and relative risks from large observational studies to quantify the health and environmental impacts of meeting adult and child recommended daily protein intakes in urban Addis Ababa. We find that plant-based foods, especially legumes, would have the lowest environmental impact and substantially increase life expectancy in adults, while animal-source proteins could be beneficial for children. This context-specific approach-accounting for regional constraints and trade-offs-could aid policymakers in developing culturally appropriate, nutritionally adequate and sustainable dietary recommendations.