The global food system is a major driver of most-pressing sustainability challenges such as climate change, unsustainable resource extraction, and altered biogeochemical cycles of N and P1-5. Food loss and waste is at the heart of the problem6,7. With 1/3 of food uneaten but lost/wasted, not only do resources consumed in producing the food ‘go down the drain’ but also the wasted food continues to brew health and pollution problems8,9. Here we show that food waste recovery and upcycling can effectively mitigate food’s unintended consequences. Using global primary data, we estimated that recovering and treating food waste via composting, anaerobic digestion, or feed-making technologies could reduce carbon footprints by 614–1041 Mt CO2-eq, compared to landfill baseline, potentially offsetting global food system’s climate burden by 4.5–7.6%. Up to 6.6 Mt nutrients could be re-captured for soil-crop-based upcycling. The feed-making option could generate up to 155.6 Mt novel feeds for animal-based upcycling, potentially replacing 41% and 9% of maize and soy in global livestock feeding. Feed grain replacement can bring an array of cascading benefits such as land and fertilizer spared and pollutions avoided, which are evaluated for the U.S. and China as case-study countries.

Elevated inputs of nitrogen (N) fertilizer have played a key role in feeding an increasing global population, but also caused many environmental problems due to emissions of reactive N (Nr) to air and water worldwide, especially in China. To better understand the improvements to N management required to reduce impacts in China, we compiled a long-term N budget over the period 1961-2018, quantified historic changes in N inputs, crop uptakes and losses, and compared them with required N inputs to satisfy food security and critical N inputs to protect the environment in view of acceptable losses of ammonia to air and nitrate to water. Nitrogen inputs required to satisfy the food demand of China were 14, 21, 27 and 29 Tg N yr-1 in 1961, 1980, 2000 and 2018, respectively, while the actual N inputs were 4, 25, 39 and 48 Tg N yr-1, respectively, exceeding the required input after 1980. Since 2000, the actual N inputs also exceeded the critical N inputs in view of ammonia emissions to air (35 Tg N yr-1) and nitrate leaching to groundwater (28 Tg N yr-1) that are needed to protect biodiversity and human health. We show that a reduction in N input from 48 to 31 Tg N yr-1, which reconciles food production with environmental safety, can be achieved through the effective recycling of manure, balanced N fertilization and integrated soil-crop system management. Such a 'win-win' would improve air and water quality and protect the environment and human health through improved resource use efficiencies, reduced N fertilizer use and decreased Nr losses.