The current global food system is inefficient, with significant competition for resources between food and feed production. A substantial portion of arable land (up to 40%) and cereal production (over 30%) are dedicated to animal feed, along with approximately 23% of captured fish. This competition reduces system efficiency and increases environmental costs. Utilizing food system by-products—secondary products from food production—as animal feed is proposed as a solution to enhance resource use efficiency, reduce food-feed competition, and increase food system circularity. This approach offers the potential for reduced environmental pressure on land and freshwater ecosystems, decreased greenhouse gas emissions, and lower fertilizer use. While some by-products have challenges (e.g., low digestibility, poor protein quality), processing or additives can improve suitability. This study aims to assess the global potential of this strategy, overcoming limitations of previous research by utilizing comprehensive and harmonized datasets of feed material flows and by-product availability. The study advances the field by providing a detailed quantification of global food system material flows, a comprehensive analysis of by-product flows, and an assessment of the replacement potential of food-competing feedstuff with by-products while considering nutritional constraints in both livestock and aquaculture.

Existing literature sporadically estimates material flows related to food system by-products, lacking a comprehensive understanding. Studies have assessed individual by-product potential within specific systems and analyzed livestock production scenarios sustained by non-food-competing feedstuffs. This study builds upon this work by quantifying global food system material flows, analyzing by-product availability, and assessing the replacement potential of food-competing feedstuff with by-products, considering regional availability and nutritional limitations in both aquaculture and livestock sectors. Nutritional constraints are based on a literature review of feed experiment studies.

The study employs a four-phase analysis. First, it quantifies global food system material flows, including feed use in livestock and aquaculture and potential by-product production. Data from various sources (FAOSTAT, GLEAM, etc.) were combined and harmonized for the period 2016-2018. The focus was on food-competing feedstuffs (cereals, oilseed oils, pulses, whole fish). Second, regional by-product availability was assessed by subtracting current feed use from potential production, assuming all unused by-products are available for feed. Four by-product categories were considered: crop residues, crop processing by-products, livestock by-products, and fish by-products. Third, the study determined the extent to which by-products can replace food-competing feedstuffs based on a literature review of feed experiments, ensuring no negative impact on productivity (except for cereal replacement with crop residues in cattle, which considers reduced productivity). Fourth, the replacement potential was calculated, combining regional by-product availability with nutritional requirements. Finally, potential increases in global food supply were estimated, assuming all freed feedstuffs are redirected to human consumption. Uncertainty analysis was performed using Monte Carlo simulations to account for uncertainties in input data. The study considered regional availability of by-products, assuming intra-regional trade but excluding inter-regional trade. The analysis focused on replacing food-grade feed use with by-products having similar nutritional profiles.

Approximately 15% (940 million tons dry matter) of total livestock and aquaculture feed consisted of food-competing feedstuff. Cereals formed the largest portion of food-competing feed use, with maize being the most significant. Fish products were crucial protein and fat sources. The availability of food system by-products was estimated, showing that only small shares of crop residues and livestock by-products are currently used as feed, while oilseed meals and a significant portion of crop processing by-products are already used. The highest theoretical potential for increased feed use lies in crop residues. Regional variations in by-product availability were identified. Considering replacement constraints (nutritional requirements and regulations), up to 11-12% of food-competing feedstuff could be replaced globally without productivity loss, rising to 25-29% when including crop residues and accepting productivity reductions. This replacement could free 430-650 × 10¹² kcal and 17-26 million tons of protein for human consumption, representing 5-7% and 7-11% of the current global food supply, respectively. Significant quantities of cereals, vegetable oils, pulses, and fish could be redirected to human food use. In the maximum replacement scenario, most cereal and sugar processing by-products would be utilized, while crop residues, fish by-products, and livestock by-products would remain largely available for other uses. The replacement of cereals offers the highest potential for increasing the global food supply; however, whole fish, pulses, and oilseed oils also contribute substantially to improved human nutrition.

The findings demonstrate the significant potential of increasing food system by-product utilization in animal feeds to enhance global food supply, complementing previous scenario-based assessments. The study quantifies the potential for reducing food-competing feedstuffs across the global food system. Regional variations in this potential highlight the role of global trade in enhancing by-product availability. The replacement potential could be further increased by considering food waste and former foods. However, several challenges exist, including by-product availability, regulations (e.g., bans on intra-species feed recycling), nutritional limitations of some by-products, and the need for infrastructure for processing and storage. Processing by-products or utilizing livestock species that can consume lower-quality feeds can improve their value. Consumer preferences and the need for processing less desirable fish species for human consumption should also be considered. Prioritizing food production over other uses of biomass (e.g., bioenergy) might be necessary.

The study highlights the substantial potential for increasing the global food supply by upcycling food system by-products and residues into animal feeds. While various challenges remain, this approach, coupled with other measures, represents a crucial step towards more sustainable and circular food systems. Future research should focus on broadening the range of by-products considered, developing a more comprehensive trade model, and conducting detailed local-level studies to account for social and economic factors.

The study acknowledges limitations in data sources and their inherent uncertainties. The uncertainty analysis provides ranges but does not fully capture all potential variations. Inter-regional trade was not fully considered, potentially underestimating the replacement potential in some regions. The combined effects of using multiple replacement materials in animal diets require further investigation. The results are considered theoretical, requiring further local-level studies to assess practical replacement potential, considering social and economic factors.