Several dietary guidelines are developed that propose limiting the intake of animal protein to stay within planetary boundaries and improve human health. Simultaneously, circular food systems are receiving significant attention in the European Union as an option to improve the current food system. In a circular system, animals are solely fed with low-opportunity-cost-biomass (LCB), resulting in substantially fewer animals and reduced supply of animal-sourced nutrients to humans. We assessed

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... her this circularity principle within the EU-28 is compatible with the recommended animal-source food consumption in healthy and environmentally friendly dietary guidelines such as the EAT-LANCET dietary guidelines. Our results show that the overall quantity of animal-sourced protein in EAT-LANCET dietary guidelines can be met, but that the precise levels of inclusion of different animal-sourced foods in such a diet cannot be achieved. The EAT-LANCET guidelines recommend larger quantities of chicken meat over beef and pork while a circular food system produces mainly milk, dairy-beef, and pork. All three circularity diets outperform the EAT-LANCET diet in nutritional value while reducing GHG emissions (up-to 31%) and arable land use (up-to 42%). Careful consideration of the permissible substitutability between animal-sourced foods is urgently needed to define the role of animal products in circular human diets. In this way the consumption of animal products - based on the circularity principle of only feeding animals with LCB - benefits both human health and the environment.