Current food systems cause severe environmental impacts. Animal-source foods additionally contribute to inefficient resource use, because resources that could be used to produce human food are allocated to feed farm animals instead. This thesis investigated environmental, social, and economic impacts of current diets (Switzerland), and of different animal-source food reduction options (Switzerland, European Union). Reduction options included adhering to national dietary guidelines, to the Planetary Health Diet, and following a vegetarian diet, in combination with increased shares of organic produce and circularity principles. We found that most reduction options result in synergies for environmental, economic, and human health impacts, but potentially increase social risks. Thus, measures towards more sustainable diets should also consider improvements in social aspects, such as working conditions. Further, more transparency on the role of animal-source foods in dietary guidelines could be achieved by reconsidering their nutritional function as well as their permissible substitutability.