Sustainably feeding the next generation is often described as one of the most pressing “grand challenges” facing the 21 st century. Generally, scholars propose addressing this problem by increasing agricultural production, investing in technology to boost yields, changing diets, or reducing food waste. In this paper, we explore whether global food production is nutritionally balanced by comparing the diet that nutritionists recommend versus global agricultural production statistics. Results show that the global agricultural system currently overproduces grains, fats, and sugars while production of fruits and vegetables and protein is not sufficient to meet the nutritional needs of the current population. Correcting this imbalance could reduce the amount of arable land used by agriculture by 51 million ha globally but would increase total land used for agriculture by 407 million ha and increase greenhouse gas emissions. For a growing population, our calculations suggest that the only way to eat a nutritionally balanced diet, save land and reduce greenhouse gas emissions is to consume and produce more fruits and vegetables as well as transition to diets higher in plant-based protein. Such a move will help protect habitats and help meet the Sustainable Development Goals.

Funding: This work was supported by Food from thought: Agricultural Systems for a Healthy Planet Initiative, by the Canada First Research Excellent Fund. Grant number 000054 to MC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2018 KC et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Producing enough food for the growing human population while reducing greenhouse gas (GHG) emissions and other environmental impacts from farming is a major global challenge [ 1 – 2 ]. Proposed solutions commonly focus on boosting production by approximately 70%, increasing yields in unproductive regions, eliminating waste, and reducing meat consumption [ 3 – 5 ]. Such solutions may also help reach some of the environmental targets set by international agreements such as the Paris Climate Agreement [ 6 – 7 ] and the Sustainable Development Goals (SDGs) [ 8 – 10 ]. To date, however, there has been no serious global evaluation of whether the production of different types of food (especially fruits and vegetables) is sufficient to provide a nutritionally balanced diet for the global population. Nor is it known whether a switch towards a nutritionally balanced diet might reduce the environmental impact of food production, thus helping meet SDGs and the Paris Agreement targets. A recent paper [ 11 ], however, found that a global shift towards current Western diets, an already observed trend in many parts of Asia, could lead to increased land use by 1 Giga hectare. This suggests that at least some commonly used nutritional guidelines need to be considered in terms of their impact on environmental sustainability [ 11 ]. Building on existing studies [ 12 – 14 ], this paper explores the extent to which global food production was nutritionally sufficient for 2011 (our baseline year when the world’s population was approximately 7 billion) and will be sufficient for a population of 9.8 billion, which is expected in 2050. We do this by comparing the types of diets nutritionists recommend versus global agricultural production statistics, and then explore options for producing a nutritionally balanced global diet.

Data and methods

We begin by comparing the amount of food that is produced globally with what nutritional experts consider to be a healthy diet, and then estimate both the land use and greenhouse gas implications of switching to nutritionally recommended diets. To do this, we use a range of food and crop databases [15] along with different nutritional guidelines and recommendations [16–23] using the following assumptions.

Choice of nutritional guidelines While all nutritional guidelines are similar in that they recommend diets rich in fresh fruits and vegetables and low in sugars, different guidelines offer somewhat different advice regarding protein, dairy, starches, and grains. For instance, compared to the Harvard Healthy Eating Plate (HHEP) [18], the Canadian Food Guide (CFG) [17] suggests 27% fewer servings of fruits and vegetables, 34% fewer servings of meat/protein, but 60% more servings of dairy products and 25% more grains. Although some studies [24–28] show that the association between total fat/saturated fat and non-communicable diseases is mixed, there is a clear consensus across dietary guidelines that we should limit sugars, saturated and trans fats, oils and simple carbohydrates, and eat an abundance of fruits and vegetables. In addition, there is some speculation that nutritional food guidelines may be vulnerable to political and industry interference [29–30]. Given the controversies and discrepancies, in this study we opted to use the HHEP as it is a well-regarded nutritional guide that provides broadly consistent nutritional advice but is not linked with any particular national government or industry.

Calculating actual and recommended servings Diets are often described in terms of “servings” of different foods [17], but what constitutes a serving varies depending on the type of food. For instance, 125ml fresh or frozen vegetable is considered 1 dietary serving of vegetable, 1 slice of bread is considered 1 serving of grains and 75 g of cooked meat is considered 1 serving of protein. To calculate the actual number of dietary servings available worldwide, we used 2011 data from the United Nations’ FAO Food Balance Sheet [15] (S1 Table) and categorized the individual foods into the five broad food categories of the HHEP: whole grains, fruits and vegetables, protein, milk and oils. Given discrepancies in terms of what constitutes a fruit versus a vegetable we opted to combine fruits and vegetables into one single category. Finally, as sugar was not part of the HHEP diet, we considered it as a separate category. Next, we determined an average number of calories per dietary serving for each type of food using guidelines from both the Canadian Food Guide [17] and the US Department of Agriculture [23]. Finally, we divided the available daily per capita calories for each food type by the number of calories per serving. This allowed us to calculate the number of available servings per person per day for each food type. To calculate the number of servings needed to meet the HHEP requirements, we followed the following steps and assumptions. First, we interpreted the HHEP model as translating into the following recommendations: (1) 50% of our diet should be fruits and vegetables; (2) 25% should be whole grains; (3) the remaining 25% should be made up of protein, fat, and milk. Since there is considerable debate among nutritionists about specific levels of protein, fat and dairy, we assumed people following HHEP would consume: 1 serving of fat/oil, 1 serving of milk/dairy, and 5 servings of protein to make up this 25% of the diet. Given that assumptions had to be made, the calculations presented here represent only an approximation of the HHEP diet.

Calculating the amount of land needed for existing vs. HHEP diets FAO statistics provide a breakdown of the amount of food in each food category that is used for human consumption versus livestock feed. The statistics also provide a breakdown of the amount of protein produced by the dairy sector, by livestock in the form of meat, and by plants (see details in S2 Table). These statistics were used to calculate the amount of land used for each type of food, the amount of land devoted to livestock feed versus food for direct human consumption, and for meat versus dairy (Table 1). These calculations provided a baseline assessment of the amount of land used by these various types of agriculture for the year 2011, when the world’s population was approximately 7 billion people. PPT PowerPoint slide

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larger image TIFF original image Download: Table 1. Estimation of arable land area for milk and meat production * . https://doi.org/10.1371/journal.pone.0205683.t001 Next, we compared the amount of land currently devoted to these different food groups and the amount of land that would be required under the HHEP model using 2011 statistics. The surplus (or deficit) of land for each individual food group, as well as the total amount of the arable land needed, was then calculated to show how our demands for arable land would shift under the HHEP model. To account for the growing human population, we extrapolated food production and land-use requirements using the United Nations’ mid population projection of 9.8 billion by 2050. To account for rising technological sophistication, we assumed a 1% annual increase in yield that corresponds to historic patterns in yields in FAO statistics. Finally, we estimated the impacts of adopting a HHEP diet on the total amount of arable land and the total amount of pasture land today and in the future, following the FAO definition of pasture land as “…land used permanently (five years or more) for herbaceous forage crops, either cultivated or growing wild …” (FAO 2018, page 2)[31].

Calculating greenhouse gas emissions We used a life cycle approach to calculate GHG emissions for different types of food by multiplying a food’s GHG emission factor (in carbon dioxide equivalents per kg of food) times the mass of annual global production of that food type. GHG emission factors were obtained from a database developed by Veeramani et al. [32]. Calculations were performed using SimaPro Lifecycle Assessment (LCA) software [33]. GHGs are calculated to the farm gate and include raw material extraction for agricultural inputs such as fertilizer and fossil fuels, but they do not include GHG emissions from land use change or soil carbon sequestration. The GHG estimates are meant only to provide trends related to changes in diets. Available life cycle studies and databases for foods produced under the range of conditions that occur globally [34] are limited, therefore, some emission factors are based on global data, while others come from European sources. Furthermore, GHG emissions from land use change and management, and resulting changes in soil carbon or biomass cover, are not generally included in these databases. As a result, these estimates are mostly useful for looking at changes in the direction of emissions rather than providing an accurate assessment of the absolute amounts of GHGs emitted for different food products. A global emission factor for fish was estimated based on global fishing fleet fuel consumption [35], since this is the main source of GHG emissions in the wild-caught fish supply chain. Fish from aquaculture operations was not considered due to lack of globally representative data on this system. GHG emissions associated with cattle production depend on how the cattle are raised, so an average emission factor was developed to approximate both “best” and less efficient management practices in the major cattle-producing countries [36–37]. It was assumed that 50% of cattle were under best management and 50% under conventional and less efficient practices. This is likely to underestimate emissions as more than 50% of the world’s cattle are located in Brazil or India [38], where practices are still relatively inefficient. Finally, as emission factors in the LCA databases are based on live weight, the following conversions were used to relate carcass weight to live weight: 52% for bovine meat, 56% for sheep and goat, 72% for poultry [39], and 50% for fish [40]. The LCA databases used to obtain GHG emissions do not include all the food types reported in the FAO food balance sheets. Therefore, whenever a food type was missing, the mass of that food type was redistributed amongst the available food items. For example, edible offal and mutton/goat are not listed in the LCA database, so the amount of these foods was redistributed amongst the available animal products. The annual consumption, on a mass basis, of each food for two population sizes, and HHEP versus current diet, was determined based on an existing methodology [16] modified to consider the number of servings required to meet the HHEP diet. Furthermore, we set the proportions of the different food items in the HHEP diet to match the proportions in the FAO production data; for example, if beef was 50% of total animal protein in the FAO 2011 production statistics, we maintained the same ratio in the HHEP diet even though HHEP recommends red meat only 2 times per week. Hence (as discussed below) the analysis overestimates the impact of meat because it retains current proportions of red meat. While the inclusion of fish in the diet does not affect land use patterns, it does have significant implications for GHGs. However, nutritional recommendations for the ideal amount of fish differ, with the HHEP recommending 1–2 servings of high-omega content fish per week [41] and the University of Michigan’s dietary recommendations suggesting 2–4 servings [42]. Here, we used 2 servings per week, which translated to 9% of the required protein servings. Overall, these assumptions introduce some uncertainty in the absolute value of the GHG emission calculations. Nevertheless, this approach provides useful relative values for the purpose of comparisons.

Scenario analysis Finally, to provide a rough estimate of the implications of different possible strategies, we estimate the impact of four possible future scenarios: A scenario where all livestock consumption is replaced by plant-based proteins;

A scenario where consumers reduce livestock consumption to 20% of their protein (consistent with the current ratio of meat: plant-based protein in India);

A science and technology scenario where new technologies increase crop yields;

A household food waste reduction scenario.