Upcycling biomass in a circular food system: The role of livestock and fish

Research output: Thesisinternal PhD, WU


A more circular food system is increasingly proposed to address the challenge of feeding a growing world population while limiting environmental impacts and resource use. A circular food system prioritises resources for direct food supply to avoid feed-food competition. The role of animals is to upcycle resources unsuitable or undesired for human consumption, so called low-opportunity-cost feeds (LCF) into animal-source food. This thesis evaluates the potential of various animals in upcycling LCF in a circular food system by applying an optimisation model that allocates available LCF to that combination of animals that maximise the supply of human digestible protein (HDP) to a EU-28 case study. We first explored the potential of common livestock species in the EU (e.g. pigs, laying hens, broilers, dairy cattle and beef cattle) under various productivity levels. Optimal use of LCF required livestock systems that had a high conversion efficiency (laying hens, dairy cattle), were best able to valorise specific LCF (dairy cattle for grass; pigs for food waste) and could valorise low quality LCF due to their low productivity. When, in addition, considering fish – currently the only natural source of the essential eicosapentaenoic (EPA) and docosahexaenoic (DHA) ω-3 fatty acids – while demanding EPA/DHA requirements are met, fish provide nutritious food via both capture fisheries and fish farming. Even if capture fisheries rebuilds stocks and prioritises edible fish for human consumption, it can only fulfil 40% of EPA/DHA requirements. The farmed fatty fish needed to meet these requirements depend on fisheries by-products to meet their EPA/DHA requirements and livestock slaughter by-products to meet their high fat and protein requirements. A circular food system thus requires a combination of co-dependent animal production systems, tailored to the available LCF and the desired nutrient output. As the availability of food leftovers as LCF is currently restricted by legislation and other barriers, we explored the potential of food leftovers currently not used as LCF. Potential to increase animal protein intake was highest for, currently banned, household waste (+12%) and livestock by-products (+18%) that are allowed in fish feed but currently not used and appear essential to meet human requirements of EPA/DHA ω-3 fatty acids in a circular food system. Improved use and legalisation of inevitable food leftovers can improve the resource use efficiency of both current and future circular food systems. When allowing all LCF in a circular food system, livestock and fish provide an HDP intake up to 39 g per capita per day, less than current animal protein supply but meeting 65% of total protein requirements. A circular food system, thus, requires a reduction in ASF consumption, and a change in the type of ASF we consume, where fish and milk become more prominent. While the used food systems approach illustrates the potential of animal production in a circular food system, it provides little direction to farmers in achieving sustainability objectives. Currently, they base their sustainability strategies on supply chain life cycle assessments (LCA) that does not account for feed-food competition. In a case study of a novel egg production system, such LCA underestimated the environmental benefit of feeding only LCF with 57% for global warming potential and 96% for land use. The proposed food-based allocation, better captures the complexity of the food system, a first step towards metrics that stimulate circularity. Besides improved understanding of our food system, such novel metrics and changed consumption patterns, the paradigm shift needed to move towards a circular food system requires that policy makers value social and economic aspects within the ecological boundaries of our planet. This way, farm animals can contribute to the resource use efficiency of the entire food system.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • de Boer, Imke, Promotor
  • van Zanten, Hannah, Co-promotor
Award date30 Oct 2020
Place of PublicationWageningen
Print ISBNs9789463954310
Publication statusPublished - 2020


  • biobased economy
  • livestock
  • aquaculture
  • biomass
  • biomass cascading
  • livestock farming


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