Assessment and scenario hypothesis of food waste in China based on material flow analysis

Field research limits the possibility of clarifying the current food waste situation in China. Material flow analysis was used to assess the magnitude and characteristics of waste in five stages from 2010–2019 by seven selected types. Wheat was wasted the most at 38%, while milk was wasted the least at 4%. During post-harvest handling and storage, processing and packaging, and consumption, wheat was wasted the most (56%, 36%, and 48%), while during production and marketing, tomatoes were wasted the most (28% and 25%). Wheat, apples, tomatoes, pork, and milk were wasted the most in consumption, while soybeans were wasted the most in processing and packaging, and freshwater fish were wasted the most in production. A scenarios hypothesis proved that a 5% reduction in each stage would reduce import demand for soybeans by 7%. This study provides a data reference and theoretical basis for food waste intervention and food security strategies.


INTRODUCTION
Food loss or waste exists at all stages of production, storage, transportation, processing, and consumption, and a large amount of food available for human consumption is lost and wasted globally. Food waste is one of the major factors affecting the security of the global food system, while also causing serious resource and environmental problems 1 . This is particularly serious for emerging economies, and the largest increase in greenhouse gas (GHG) emissions associated with food loss and waste (FLW) is found in developing economies, where food consumption patterns, as well as the amount and structural characteristics of FLW, are rapidly shifting due to urbanization and changes in diets and incomes. China has shown an alarming increase in FLW and is one of the top ten countries in the world in terms of food loss and waste and associated GHG emissions 2 , contradicting the country's efforts to feed 19% of the world's population on only 7% of the world's arable land when resources (such as water and energy) are already constrained. United Nations (UN) data show that Asia still has the highest number of people who are underfed globally (381 million) 3 . In the face of growing environmental and food security challenges, combating food loss and waste is an urgent matter.
In response to this issue, the UN has introduced Sustainable Goal 2.0 Zero Hunger, and Target 12.3, calling for a 50% reduction in food waste by 2030 at both retail and consumer levels. As the world's largest developing country and the highest-emission country with regard to carbon dioxide, China is a critical country for the world to reaching this goal. While some empirical studies have been conducted around food loss and waste, few have been conducted on the entire food supply chain and most existing studies on the topic do not include all food categories, with a particular lack of studies on waste at different stages of the food supply chain for categories such as vegetables, aquatic products, and milk. Nearly half of the studies also used out-dated data and had very limited sample sizes, which may have a great impact on the estimation of food loss and waste 4 .
Some countries have introduced relatively clear food waste reduction targets for different scenarios and sectors at the outset of their legislation. The lack of specific and clear quantitative targets in China's Anti-Food Waste Law enacted in 2021 is partly due to a lack of knowledge of the current state of waste regarding different food categories at various stages in the food supply chain. Scientific research on refined management requires different methods to address this urgent issue. To fill these research gaps, this study used the material flow analysis (MFA) technique to systematically assess the magnitude of waste at different management stages (production, postharvest handling and storage, processing and packaging, distribution, and resident consumption) for seven food categories in China, with the aim of identifying key challenges and opportunities for food waste reduction. This study also discussed the profile of soybean import management using different scenario hypotheses. Three important challenges are addressed in this study: (1) Tracking food flows along the entire food supply chain at different life cycle stages and sorting out the inventory at each stage. (2) Analyzing the waste structure of different food categories, comparing the stages and assessing the opportunity points for food waste intervention.
(3) Predicting the reduction potential of relying soybean imports. The results of this study show the utility of MFA for food waste, and suggest corresponding policy recommendations to reduce food waste, as well as support government management and policy development in this regard.
The definition of food waste varies among different research institutions and scholars. This study adopts the Food and Agriculture Organization of the United Nations (FAO) definition of FLW: food loss is the reduction in the quantity of food that occurs during the food supply process that is not subjective, and food waste is food produced for human consumption that is artificially discarded at different stages of the food supply chain (excluding non-food uses such as feed and seeds) 5 .
One study showed that food waste at the food and beverage consumption stage in China equaled no less than 4.47% of the total annual grain production in 2016 6 . By means of a wholeindustry chain tracking survey, Zhou et al. 7 found that the loss rates of the entire chain (farming, slaughtering, acid removal, splitting, transportation, retailing and storage) of pork, chicken, beef, and lamb in China were 8.1%, 11.22%, 1.47%, and 7.45%, respectively 7 . Lu et al. 8 conducted a whole-industry chain field study in China's main rice planting areas and found that the combined loss and waste rate of rice was 13.64%, with a wholeindustry chain loss rate of 8.42% and standardized loss rates of 2.84%, 1.85%, 1.21%, 1.73%, and 0.79% for harvesting, postharvest handling, storage, processing and distribution, respectively, while the rate of consumption-stage waste was 5.22% 8 . Li et al. 9 found that the loss and waste rates of the entire industry chain (production, post-harvest handling, storage, distribution and consumption) for apples and oranges were 18.56% and 17.15% respectively, with distribution accounting for the highest proportion of the total waste, about one-third 9 . Due to the difficulty of field research, there is currently a lack of whole industry waste studies on certain food categories, such as vegetables, aquatic products, and milk.
Quantitative measures of food loss are mostly based on farmer questionnaires and empirical assessments, and there is a lack of field measurements at the post-production stage. There are four approaches to investigating food waste at the consumer stage, including the bookkeeping approach 10 , the 'archeological' approach 11 , weighing of plate leftovers 12 , and inferences from secondary data 13 , each of which has its own advantages and disadvantages (Table 1). Most studies have combined two or more of these methods, and only a few scholars have conducted food loss and waste studies using the MFA method. The MFA method does not interfere with respondents, supports calculations with large sample sizes, has a higher accuracy of calculations and importantly can identify patterns of material flows, i.e., stages that are particularly characteristic of food waste 14 .
Li 15 constructed a food supply chain energy flow input-output model for China and found that the food manufacturing and processing industries consume the greatest amount of energy from coal and that increasing per capita food expenditure and population growth are the main factors driving the growth in food supply chain energy consumption 15 . Padeyand et al. 16 combined MFA and life cycle assessment methods to find high environmental impacts occurring during the handling stage in North Korea 16 . Munsol et al. (2016) derived the share of three different food consumption patterns to provide a basis for future MFA studies 17 . Munsol (2017) also used MFA for a study conducted in Japan and found that the food category with the highest loss rate was vegetables 18 . Thamagasorn and Pharino 19 conducted an MFA on food waste from flight corporate catering and found that vegetable waste accounted for 47.58% of the total food waste in this category 19 . Amicarelli et al. 20 applied MFA to assess opportunities for waste reduction in the Italian potato industry 20 . Sadeleer et al. 21 found that a small waste across the chain in Norway leads to high GHG emissions 21 . It can be found that the application of the MFA method in the field of food waste remains very limited, and a further expansion of food waste research is needed, especially in China.

RESULTS AND DISCUSSIONS Status of food waste across all stages
Due to space constraints, this study presents the complete stock, flow, and waste of seven food items at each stage in Supplementary  Table 1. From 2010-2019, wheat had the largest stock in the production chain, much higher than that of the other food categories (Fig. 1). This is mainly because most of human's typical three meals per day consist of foods that are mostly grain-based. The growth rate from 2010 to 2017 was around 2%, with a slight decrease in production in 2018 compared to the previous year. The decreasing production of pork, tomatoes, milk, apples, freshwater fish, and soybeans, in that order, is not only related to the demand of consumers but also to the characteristics of the food itself, such as fish capture production accounting for only 21% of the country's total fish production (consisting of farmed and captured fish), with 79% stemming from farmed fish. In recent years, many parts of China have launched various actions to protect the ecological environment and regulate pollution from aquaculture, and the aquaculture area has been decreasing year by year 22 , which, combined with a restrictive fishing policy issued by the Ministry of Agriculture at the end of 2013, resulted in lower production of this category compared to other food categories.
In terms of average annual waste, wheat was the most wasted food at 45.7 Mt, accounting for 38% of the total waste across the seven food groups, followed by tomatoes, apples, pork, freshwater fish and soybeans at 19%, 13%, 10%, 8%, and 8%, respectively, while milk was the least wasted at 4.3 Mt, accounting for 4% of the total. Wheat, soybeans, apples, and milk did not show significant temporal characteristics across the stages, with some fluctuations. Two food categories, namely tomatoes and freshwater fish, showed an upward trend in total waste across the five stages with an average annual increase rate of 4% and 2%, respectively. Pork showed a decreasing trend in waste over time across the five stages from 2014 onward, with an average annual decline of 2% in total waste. As economic growth and living standards improve, the amount of food waste shows an overall upward trend, with only the total amount of meat waste showing a downward trend, which this study speculates is related to the higher sales price of meat compared to other food products. According to the consumer price index for food categories released by China's National Bureau of Statistics, the price index for livestock meat has been higher than the prices of other food categories from 2016-2020, limiting the number of purchases made by consumers and reducing waste by due to consumers' economic loss avoidance 23 , making the amount of waste correspondingly lower. On the other hand, due to the popularity of vegetarianism 24 , consumer demand for meat is reduced, which, in turn, affects the overall amount of food waste. It is worth noting that 24.1Mt of wheat, equal to 19% of the total wheat production, are typically used for feed, seed, and other uses each year, meaning not all of it goes toward the residential food supply. Soybeans account for 9.3Mt, equal to 69% of production for feed, seed, and a large number of imports for animal feed. Freshwater fish amounted to 0.7 Mt, equal to 3% of the total production for other uses, and part of the protein content is also made into chemical or pharmaceutical products. There are 0.2 Mt of milk produced, equal to 0.5% of the total production in this category is that used for feed and other uses, indicating that only a small amount of milk is utilized for uses besides direct consumption. There are no uses for vegetables and fruits other than human consumption.

Characteristics of food waste by stage
The average amount of food waste by stage was further calculated for the seven food categories from 2010-2019. According to Fig. 2, it can be seen that among the seven food categories, wheat had the highest total waste, followed by tomatoes, apples, pork, freshwater fish, soybeans, and milk. Among them, wheat was wasted the most in the post-harvest handling and storage, processing and packaging, and consumption stages. Calculating the total amount of waste in each stage for the seven food categories, wheat was found to account for 56%, 36%, and 48% of waste in the post-harvest handling and storage, processing and packaging, and consumption stages, respectively. Tomato waste was the highest in the production and distribution stages, at 28% and 25%, respectively.
Wheat waste is highest due to manpower constraints and poor technology. In southern China, the wheat harvesting period is very short and the maturity period at the time of harvest is often overdue, resulting in a large amount of wheat being discarded directly into the fields due to "rush harvesting." Poor storage equipment decelerates grain losses, and in addition to the machine harvest rate of wheat being 82%, the overall quality of machinery is not high, resulting in unavoidable grain losses. This is a result of a combination of pests, diseases, and human and mechanical harvesting damage 25 . In addition, although China is the world's leading wheat producer, wheat imports are the second largest of the seven food groups in terms of production, at 4%. Wheat imports are mainly used for agricultural restructuring, where wheat-growing fields are converted to other cash crops or agricultural crops, or where farmers choose to use wheat to meet livestock feeding needs rather than maize, which has increased in price 26 . Therefore, reducing wheat waste is also an  important way to reduce the dependence on wheat imports and should be taken seriously. In recent years, consumers have shifted their diets to being more vegetarian, resulting in the over-purchase of vegetables, which, due to their perishable nature, leads to a total vegetable waste rate that is second only to wheat 27 . One of the reasons why milk was wasted the least among the seven categories is that milk processing and packaging waste amount and waste rates are both much lower than in other food categories.

Characteristics of food waste by category
The characteristics of the waste share of each food category at different stages were further examined. According to Fig. 3, it can be seen that wheat, apples, tomatoes, pork and milk have the most waste at the resident consumption stage, soybeans had the most waste at the processing and packaging stage, and freshwater fish had the most waste at the production (fishing) stage. This study combined the United Nations Environment Programme's Food Waste Index 2021 report with the World Bank's country income grouping criteria 28 and found that waste at the consumption stage is common across many continents and countries of different income levels, with no significant pattern, with China's food waste at the consumption stage being particularly serious, ranking first in terms of food waste (Supplementary Table 2). Specifically, wheat was wasted the most at the consumption stage, accounting for 51% of the waste in total food supply chain process. This phenomenon is mainly related to the typical Chinese food culture and the inadequacy of the relevant regulatory system. Influenced by a sense of mianzi, a "show-off" and "luxury" consumption value, consumers tend to over-order to gain mianzi and show their hospitality to their guests. The more food they order, the stronger their economic power and the higher their social status are perceived as, and they, therefore, prefer to order more leftovers when ordering, believing that leftovers carry good luck 29,30 . On the other hand, China's first Anti-Food Waste Law was introduced not long ago, and the regulatory process for food waste is still immature. Before that, food waste reduction relied solely on consumer consciousness, leading to serious food waste among consumers, with the consumption stage becoming where the largest part of most food waste rates can be found 31 . Soybeans were wasted the most during processing and packaging, accounting for 46% of the total food waste at this stage. This is because soybean products have a more complex production processes and longer processing lines, increasing the probability of waste. Apples had the most waste at the consumption stage at 34% of the total waste at this stage. This is because apples do not require much processing after picking and have lower packaging losses, but there can be waste caused by consumer rejection of sub-optimal goods, such as a reluctance to buy or eat fruit items that are "ugly" in appearance or not brightly colored 32 . Tomatoes had the most waste in the consumption stage at 34% of the total. This is often due to the fact that tomatoes have similar characteristics to fruit, do not require much processing, and have lower packaging losses. However, compared to industrialized countries, the infrastructure and storage facilities for fruit and vegetables, such as cold storage, are poor in low-income countries, resulting in losses during post-harvest handling and storage 33 . The proportion of pork wasted in distribution was 27%, which is mainly due to the high perishability of meat, which leads to high waste in distribution and transportation. It is estimated that food transport in China accounts for nearly 30% of the total road transport of goods 15 , and the distance over which food is transported increases the probability of spoilage. Freshwater fish had the most waste at the production (farming or fishing) stage with 37% of the total waste at this stage. It is related to the lack of advanced fishing technology. Milk was wasted the most at the consumption stage with 45% of the total waste at this stage. The waste of dairy products is mainly due to consumers' sensitive perceptions of health risks and the tendency to discard goods that are close to their expiry date or past their optimal taste date for safety and health reasons, even if they are still edible 34 .
The impact of food waste reduction on import quantity The production utilization rate for each food group was calculated by comparing the amount of total waste with the amount of production, with larger ratios indicating lower production utilization rates. As can be seen in Table 2, soybeans have the lowest utilization rate, mainly because China is more heavily reliant on soybeans for imports, with less domestic production and rising import rates. According to data released by the General Administration of Customs of China, China imported 48 Mt of soybeans in the first half of 2021, which is an increase of 8% compared to the same period last year. The need to ensuring food security makes it urgent to achieve self-sufficiency in grain production and given the waste that exists at various stages of the soybean food chain, this study further hypothesizes scenarios to predict the impact of reduced waste at various stages on soy imports through MFA. Given that the UN 12.3 target calls for a 50% reduction in food waste at the retail and consumer levels by 2030, this study assumes a scenario of a 5% reduction in waste at each stage of the soybean import requirement in consideration of the current reality (Fig. 4).
It is clear from the graph that a significant proportion of soybeans are used for feed, so it is important to increase food selfsufficiency and reduce dependency on imports. According to the study results, a 5% reduction in waste across all five stages has a relatively large impact on imports, specifically, resulting in a 7% reduction in imports, meaning that the role of waste reduction in reducing the dependency on imports cannot be ignored.
Based on the findings of this study, the following policy recommendations are made.
(1) Food waste reduction targets should be set by categories and stages and key stages should be targeted for enhanced intervention. Wheat stood out in the total amount of food waste at different stages. Disease, poor infrastructure, and  inefficient machinery and equipment are the main causes of grain loss 35 , so new technology development and application should be vigorously promoted. The infrastructure for grain processing, storage and transport should be renovated, corresponding new equipment should be developed, advanced and rational processing equipment should be encouraged, harvesting efficiency should be optimized, and wheat should be entrusted to national storage units and grain banks with better storage conditions. Traders should further implement half or small portion sizes of staple foods, allow customers to choose whether they need staple foods or not, and not bundle packages for sale in order to reduce wheat waste. Tomatoes, which had the second highest total waste amount among the seven food groups, which were also on the rise, should be another key area of concern for researchers. Consumers need to better plan their purchases, buy only as needed, and store tomatoes well to prevent their spoilage and waste. Further research into the waste determinants of both wheat and tomatoes would be beneficial for improving the efficiency of waste reduction. In addition, the total amount of pork waste is showing a downward trend, and further research on the whole meat chain should be conducted in the future so that the appropriate control policies for this food category can also be applied to intervention policies for other food items, such as wheat and tomatoes. For example, food prices could be raised appropriately, financial penalties could be imposed on enterprises or individuals with severe waste in this category, and regional development and reform commissions could promote metering and charging for the disposal of residential food waste at various levels to draw attention to the food waste problem. In the case of freshwater fish, which is showing an upward trend in waste, greater control efforts could be beneficial, and targets should be set according to the stages of waste, with a focus on the farming and fishing sectors. Stakeholders that are relatively advanced in their actions against food waste, such as farmers and large supermarkets, are typical model individuals and units who can promote the concept of saving food and reducing waste in order to encourage other farmers, merchants, and others to take the initiative to reduce food waste. (2) The food supply system should be optimized and an efficient food supply chain system should be established. This study found that food waste is much higher at the consumption stage for all types of food than at other stages, so optimizing the end of the supply chain, i.e., reducing waste at the consumption stage, is crucial. Due to China's increasing urbanization and rapid economic growth, the average frequency of eating out has increased, increasing the chances of food waste occurring, which, combined with China's special food culture, has led to a severe form of waste at the consumption stage 36 . The government should, therefore, strengthen publicity and education to change the current unsustainable consumption concepts, promote healthy and green consumption, and reduce the number of unwanted food purchases. Food waste in the upstream subjects of the food supply chain can be indirectly reduced by curbing the amount of unreasonable demand at the consumption stage. In terms of food recycling at the consumption stage, the construction and localization of food banks should be strengthened and transformed. In March 2015, the Shanghai Oasis Food Bank joined the Global Food Bank Network as the only food bank in China mainland 37 , but the Oasis Food Bank has not been very effective in China. In the future, greater promotional efforts are needed to improve the recycling process at key waste points to increase food utilization and waste recycling. In addition, this study found that wheat is the most severely wasted of the seven food groups in post-harvest handling and storage, processing and packaging, and consumption. In this regard, the government should promote the intelligence of the wheat supply chain, encourage the reasonable and moderate processing of wheat, and make comprehensive use of processing its by-products. Tomatoes have the greatest proportion of waste among the seven food categories in terms of production, transport, and distribution. In response, digital monitoring of the tomato logistics process should be strengthened to prevent the risk of corruption in cold chain transport or general logistics transport of fresh foods, which is leading to the waste of human, material, and financial resources invested in the upstream of the food chain. At the same time, consumers should be encouraged to buy local foods to reduce food spoilage and waste caused by transporting across large distances. (3) A system of green supply standards for food products should be developed. A green food supply chain refers to the implementation of green concepts throughout the life cycle of foods from production, processing, storage, and packaging to transportation, consumption, and even recycling, taking into account economic, environmental, and social development 38,39 . The current green food supply chain emphasizes the safety and hygiene of food, but does not focus enough on improving the utilization of food resources, promoting green food consumption and reducing the environmental impact caused by food waste.
In this regard, this study suggests that in terms of green processing, a strict selection of processing equipment, control of the environment in processing sites, and avoiding waste from excessive processing is necessary. In terms of green logistics, reasonable route planning and packaging, combined with a consideration of the characteristics of food and a scientific selection of storage locations and forms, such as cold-chain storage and transportation of pork, are recommended. The level of green marketing, is determined by the joint efforts of all relevant subjects in the supply chain 40 and the importance of green interactions with consumers to avoid over-marketing that leads to overbuying by consumers, especially for foods with short shelf lives, such as milk. This study found that milk had the least total waste and relatively more waste in the processing and packaging stages. Therefore, research on this category, beyond the processing stage, should be strengthened, by transferring methods and approaches to reducing waste in milk and establishing a system of green standards suitable for different food groups at different stages of the supply chain. It is important to note, however, that in 2017, the world's thirteen largest dairy companies produced over 338 Mt of GHG, which is more than the carbon emissions of the two greatest global fossil fuel emissions, and in 2020, the equivalent of the entire UK's emissions. Ninety percent of these emissions come from dairy cattle, and because cows eat a lot but struggle to digest it, the enteric fermentation and manure storage of dairy and beef cattle in China results in the production of 1.09 tons of methane per year 41 . The government should, thus, promote the entire dairy industry chain to respond positively to the "carbon neutrality" target, especially at the upstream production end, to improve the processing of dairy cattle's forage and increase the nutritional utilization of feed to reduce methane production. (4) An alternative way of non-food consumption of soybeans should be identified. China is the largest importer of soybeans worldwide 42 , and there is a gap between the level of soybean production in China and the international level, mainly in terms of cost and quality. Soybeans are a land-intensive crop, and Chinese soybean farmers' lands have an average size of only 660-1300 square meters and the degree of farm mechanization and standardization is far below the international standard. Soybean prices are influenced by the international market and farmers' profit margins as the final output and are extremely compressed since they have neither the capital nor the incentive to expand and improve production. On the cost side, the cost of growing soybeans in China is much higher than in the US, for example, and the small scale of cultivation leads to high logistical costs 43 . While China's domestic production is declining, the population's consumption of soybeans is rising, accounting for more than 30% of the world's soy consumption 44 . In response, soybean breeding efforts should be strengthened to produce more high-quality wild soybeans. In addition, arable land subsidy policies should be improved, and an insurance system for soybean farmers should be introduced to ensure a certain size of soybean planting areas, and large-scale soybean production should be promoted. Further, a standardized soybean cultivation technology system should be established and the selfsufficiency rate of soybeans should be increased. In addition, imported soybeans are mainly used as the key source of feed protein for livestock and poultry farming, as well as soybean oil for residential consumption 45 . Therefore, looking for alternatives to soybeans for feed and seed and increasing efforts to promote low-protein diet formulations for the farming industry to reduce consumption for other uses is criticak. A moderate use of oil is good for human health 46 and encouraging healthy consumption by the population to reduce the excessive use of soybean oil for consumption is important. This study also found that soybeans are severely wasted in processing stage, indicating that the focus should be on processing and accelerating soybean processing technology and innovation. Soybeans that do not meet the standards for human use can still be used as feed. Soybeans wasted at the processing stage should, thus, be recycled and used to feed livestock or for resource use. The government and soybean industry associations should play a role in supporting, guiding, monitoring, and servicing China's local soybean enterprises. MFA is often used to describe material cycles, both stocks and flows, in order to achieve sustainable material management, such as material recycling and reclamation 48 . The analysis of the food supply chain presented in this study is an industrial sector material flow analysis and was conducted using STAN 2. Definitions and system boundary The first step in an MFA is to establish clear boundaries. The spatial boundary for this study is China (its country code is 351 in the FAO), including mainland China, Hong Kong, Macau, and Taiwan. The study period is from 2010 to 2019 (which is the latest data reported). The system boundary covers the food supply chain from agricultural production to pos-tharvest handling and storage, processing and packaging, distribution, and consumption. Imports and exports of food also affect changes in quantities within the supply chain, so data from these two stages are taken into account in this study. According to data disclosed by the National Bureau of Statistics, most of the food products imported to China are unprocessed foods, which means imports occur after production and before processing, while the food products that are exported are often processed foods, so imported food is included in the processing and packaging stage and exported food is included in the distribution stage. In addition, there are feed, seed, and other non-food uses of some foods, and these quantities are excluded from the production stage. In this study, only the edible part offood was considered. The food categories were defined with reference to the FAO classification and the People's Republic of China agricultural industry standard NY/T 2137-2012 "Classification and Computer Coding of Agri-Product Market Information" 49,50 . Combining the food consumption characteristics of Chinese consumers and information from previous studies 51 , seven different types of food were selected: wheat for the grain category, soybeans for pulses, apples for fruits, tomatoes for vegetables, pork for meat, freshwater fish for aquatic products, and milk (liquid) for the dairy products category. It should be noted that these seven food groups, with the exception of wheat, are the most consumed food items by Chinese people in the same categories (Supplementary Table 3). For the grain category, wheat was chosen because it is the most widely distributed food crop in the world, and data from the Organization for Economic Co-operation and Development database show that China was the world's leading producer and consumer of wheat from 2010 to 2019, and the study of wheat waste is important for China, as well as for other countries. The framework for the MFA is shown in Fig. 5.

Data sources
The data are mainly derived from the Food Balance Sheets, produced annually by the FAO, which draws primarily on countrylevel data on production and trade of food commodities. In addition to food-by-food information, the Food Balance Sheets of FAO (2004) provides estimates of the total food availability by aggregating the food components of all commodities, including fishery products 52 . The definitions of terms included in this study are shown in Table 3.

Method for calculations
In terms of the mechanisms by which food losses and waste occur, the main stages that currently generate food waste include Fig. 5 Diagrammatic representation of food loss and waste at various stages of the food supply chain. The flow paths of the seven food categories in the material flow analysis system, the food supply chain from agricultural production to postharvest handling and storage, processing and packaging, distribution, and resident consumption across five stages. There are feed, seed, and other uses (non-food) uses of food in the handling stage. Food imports occur in the processing and packaging, while, exports occur in the distribution and tourist consumption in the consumption stage. S refers to stock, F refers to flow, W refers to waste, and k refers to the waste rate in a stage. Table 3. Term used in MFA.

Production
Whether contained within or outside the agricultural sector, i.e. including non-commercial production and production from vegetable gardens.

Stock Variation
Includes changes in government stocks, changes in stocks of manufacturers, importers, exporters, other wholesale and retail merchants, transport and storage businesses, and changes in farm stocks during the study period.

Processing
Refers to grain milling, feed processing, industrial, slaughtering and meat processing, fish processing, and processing of foodstuffs such as vegetables and fruits, carried out after the production stage

Consumption
The number of foodstuffs that people have to buy to maintain their basic living.

Feed
Refers to the amount of relevant food available for the feeding of livestock and poultry during the study period

Seed
The amount set aside for seeding or planting (or generally for breeding purposes, e.g. eggs for hatching and fish for bait) during the study period Other uses (non-food) Refers to the amount of commodity used for non-food purposes, e.g. oil for soap.
Tourist consumption Refers to tourist consumption by non-domestic residents and should not be included in resident consumption S. Jiang et al.
production (including agriculture and fisheries), post-harvest handling and storage, processing and packaging, distribution, and consumption (excluding tourist consumption). In this study, the relevant formulas were obtained based on a combination of the law of conservation of mass and previous studies 53 . It should be noted that given the perishable nature of food and the interview survey with the National Food and Strategic Reserve Administration of China, stored food will still flow through the supply chain to the consumption stage within a certain period of time and, therefore, it is assumed that the food system considered in this study is a steady-state system with no accumulation or stockpiling of food outside of the system. The waste rate k-values for each stage are shown in Supplementary Table 4.
0 ¼ S 3 À I À S 2 (3) 0 ¼ S 5 þ T À S 4 (6) Reporting summary Further information on research design is available in the Nature Research Reporting Summary linked to this article.