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Cite This: Environ. Sci. Technol. 2019, 53, 7694−7703

Country-Specific Sustainable Diets Using Optimization Algorithm Abhishek Chaudhary*,† and Vaibhav Krishna‡ †

Department of Civil Engineering, Indian Institute of Technology (IIT) Kanpur, 208016 Kanpur, India Department of Management, Technology, and Economics, ETH Zurich, 8092 Zurich, Switzerland

‡

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S Supporting Information *

ABSTRACT: Current diets of most nations either do not meet the nutrition recommendations or transgress environmental planetary boundaries or both. Transitioning toward sustainable diets that are nutritionally adequate and low in environmental impact is key in achieving the United Nations’ Sustainable Development Goals. However, designing region-specific sustainable diets that are culturally acceptable is a formidable challenge. Recent studies have suggested that optimization algorithms offer a potential solution to the above challenge, but the evidence is mostly based on case studies from high-income nations using widely varying constraints and algorithms. Here, we employ nonlinear optimization modeling with a consistent study design to identify diets for 152 countries that meet four cultural acceptability constraints, five food-related per capita environmental planetary boundaries (carbon emissions, water, land, nitrogen, and phosphorus use), and the daily recommended levels for 29 nutrients. The results show that a considerable departure from current dietary behavior is required for all countries. The required changes in intake amounts of 221 food items are highly country-specific but in general point toward a need to reduce the intake of meat, dairy, rice, and sugar and an increase in fruits, vegetables, pulses, nuts, and other grains. The constraints for fiber, vitamin B12, vitamin E, and saturated fats and the planetary boundaries for carbon emissions and nitrogen application were the most difficult to meet, suggesting the need to pay special attention to them. The analysis demonstrates that nonlinear optimization is a powerful tool to design diets achieving multiple objectives.

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United Nations’ sustainable development goals.9 Dietary changes provide new opportunities for individual nations to complement their other efforts toward achieving food sustainability10 such as improvement in agricultural production, closing yield gaps through intensification,2 or reducing food losses and waste.11,12 As the food consumption patterns have implications for both nutrition/human health and environmental issues, it is increasingly recognized that addressing them separately might lead to unintended consequences. For example, Chaudhary et al.9 showed that while shifting to vegetarian or vegan diets globally can substantially reduce food related carbon emissions and water use, it can lead to deficiency of certain micronutrients (e.g., vitamin B12, selenium, calcium) that are currently supplied by animal-based foods, and therefore, any recommendations to shift toward plant-based foods for achieving environmental goals might need to accompany micronutrient supplementation recommendations as well. Others have found that diets low in GHG emissions tend to be lower in micronutrients and higher in sugar

INTRODUCTION The food sector is one of the major contributors to global environmental degradation, contributing ∼30% to the total global greenhouse gas emissions, 70% to the total freshwater withdrawals, and 40% to Earth’s total land use.1,2 Application of nitrogen (N) and phosphorus (P) fertilizers for crop production causes eutrophication and dead zones in marine systems with negative impacts on aquatic biodiversity.3,4 If current trends continue, the food related environmental impacts are expected to increase in next 30 years due to a growing population and the consequent increase in demand for emission intensive products such as meat and dairy.5 At the same time micronutrient deficiency (“hidden hunger”) affects over 2 billion people worldwide,6 leading to impaired immunological functioning, retarded physical and cognitive growth, increased risks of noncommunicable diseases, and negative impacts on the economic growth for nations. 7 Indeed, diet-related diseases are the largest contributor to both human deaths and disability around the world.8 Transitioning to sustainable food consumption behaviors (demand-side interventions) can contribute significantly toward improving global nutritional/health standards while reducing anthropogenic environmental footprint and is therefore integral to achievement of at least 12 of the 17 © 2019 American Chemical Society

Received: Revised: Accepted: Published: 7694

December 9, 2018 May 24, 2019 May 30, 2019 May 30, 2019 DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703

Article

Environmental Science & Technology content.13 The United Nations’ 2030 sustainable development goals (SDGs)14 also call for taking a systems approach while designing any national or global policies targeted at consumers on changing their current dietary patterns in order to avoid trade-offs across different environmental, economic, and social goals. Previous efforts to design a “sustainable” diet considering both the nutrition and environmental aspects have employed either a stylized approach or an optimization approach. The stylized approach starts with “recommended intake levels” of different food groups (e.g., total energy = 2300 kcal/day; red meat ≤14 g/day; legumes ≥50 g/day; vegetables ≥300 g/day and so on) that are based on environmental and food security objectives or available evidence on healthy eating.15 In the next step, the current intake amounts of certain food groups are adjusted upward (e.g., for fruits, vegetables, legumes) or downward (e.g., sugar, red meat) to meet these recommended levels. In the last step, the intake amounts of rest of the food items are increased or decreased so that the of the total energy intake is equal to the recommended level. For example, recently, the EAT-Lancet Commission on Healthy Diets from Sustainable Food Systems16 presented a universal “healthy reference diet” containing the recommended intake levels (in g/day as well as kcal/day) for several food groups that are in line with available evidence on healthy eating (based on long-term epidemiological, clinical, and other data). Starting with the current diets, Springmann et al.15 used the stylized approach, and these recommended values to design flexitarian, vegetarian, vegan, and pescatarian diets for different countries. However, their flexitarian diets designed using a stylized approach fell short of daily recommended levels for certain micronutrients (riboflavin, calcium, and vitamin B12).15 Moreover, there remains a possibility that recommended diets, though nutritious and environmentally friendly, might deviate too much from current diets and thus might not be acceptable at cultural or individual levels.17 Designing sustainable diets that are environmentally sustainable, nutritionally adequate, economically affordable, and culturally acceptable in the region thus remains a formidable challenge.18 Application of optimization algorithms offers a potential solution to the above challenge of designing region-specific sustainable diets that achieve multiple objectives. The optimization approach obtains the sustainable diet by meeting a predefined objective (e.g., minimize the deviation from current intake amounts) under several nutritional, cultural or environmental constraints. In contrast with the stylized approach, the optimization approach uses the recommended intake levels of micro and macro nutrients (e.g., protein ≥52 g/day) instead of recommended intake levels of food groups. To our knowledge, Jalava et al.19 remains the only global scale study to obtain a recommended diet through an optimization algorithm for 176 countries. However, their analysis was limited to meeting the recommendations for daily dietary energy and macronutrient (protein, fat, carbohydrate, sugar, fruits, and vegetables) intake and did not take into account the recommendations for micronutrient intake or any environmental objectives/constraints. Other studies using optimization have shown encouraging results but are either limited to a particular country and typically employ selected environmental indicators (e.g., GHG emissions) or nutrients (e.g., protein, iron, zinc).20−26 Including multiple environmental indicators and nutrients in the optimization problem is

important because diets minimizing a particular environmental aspect or meeting requirements of selected nutrients might lead to trade-offs with other environmental indicators or nutrient requirements. For example, a diet minimizing the GHG footprint and meeting protein may require reduction in milk intake but this might lead to calcium deficiency.20 These national case studies used different scenario designs, optimization algorithms, constraints, and environmental footprints, all of which complicates comparisons between studies. None have assessed whether the environmental footprints of optimized diets are below the quantitative planetary boundaries, which if transgressed increases the risk for harm to the stability of the Earth system and thus human health.1,5,27 In the absence of planetary boundaries for environmental pressures, previous optimization studies have adopted particular national targets (e.g., a 30% reduction in carbon footprint from current levels) as constraints.26 In such cases, it is not clear whether the environmental footprint of the optimized diet is below the per capita planetary boundary. However, the use of optimization algorithm as a means to derive sustainable diets has several challenges. It is possible that the algorithm would not converge to an optimal (feasible) solution at all for certain countries because of conflicts between the nutritional, environmental, and cultural constraints (e.g., to meet the vitamin B12 recommendation in a particular country, red meat intake needs to increase three times than current levels but the cultural constraint does not allow this, and thus, the algorithm terminates and no feasible solution is obtained). It remains to be tested whether there exists a suitable optimization algorithm to obtain a sustainable diet for all countries under well-defined and consistent multiple constraints? Here, we apply a nonlinear optimization algorithm to identify country-specific diets that meet the WHO recommendations15,28−30 for daily intake levels of 24 essential nutrients and four nutrients of health concern (total fats, cholesterol, saturated fats, and sugar)9 as well as comply with the recently available daily per capita planetary boundaries for five environmental domains: greenhouse gas emissions, freshwater use, cropland use, nitrogen application, and phosphorus application.1,5,27 The objective function and four acceptability constraints ensure that the optimized diet deviate minimally from current dietary behavior. Our results increase the evidence base beyond existing national case studies by using a study design that applies consistent set of constraints and algorithm for all countries. Moreover, a global quantitative comparison showing which country’s current diet is farthest or closest from sustainable is lacking. By considering the difference in optimized and current intake amounts of all food items, we quantify how much each country’s current dietary behavior needs to change in order to achieve a sustainable diet.

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MATERIALS AND METHODS Current Dietary Intake Data. We obtained the data on the national level supply of 221 food commodities (g capita−1 day−1) for the year 2011 and 152 countries from the Global Expanded Nutrient Supply (GENuS) database.31 The GENuS database was created by expanding the 94 aggregated food categories of FAO’s food balance sheet data using FAO production and trade data for individual commodities32 and correcting for nonedible food mass (e.g., bones, shells, peels). For example, while the FAO’s food balance sheet only provides 7695

DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703

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Environmental Science & Technology the annual supply of broad aggregated categories such as ‘Vegetable, other’, ‘Fruits, other’, ‘Cereals, other’, ‘Meat, other’ or ‘Pulses, other’ ‘Roots, other’, ‘Spices, other’ etc., the GENuS database provides the supply of all individual commodities within these broad categories (e.g., for spinach or eggplant under the ‘Vegetable, other’ category or for grapes, kiwi, or pears under the ‘Fruits, other’ category). Knowing the supply of individual commodities is important for any nutritional assessment because the micronutrients such as vitamins or minerals can vary a lot from one individual commodity to the other within the same broad food group. The GENuS food supply amounts refer to the edible weight of food leaving a retail outlet or otherwise entering the household. We converted the food product supply values to actual consumption (intake) values by correcting for household waste using conversion factors from Gustavsson et al.33 This gave us the national average daily per capita intake estimates for 221 food items. Current Nutrient Intake. To obtain the amounts of daily per capita calorie and nutrient intake, we multiplied the food consumption values (g capita−1 day−1) with the nutritient content (e.g., g protein per g of milk) of individual food items from the region-specific nutrient composition tables provided by the GENuS database.31 Six national and regional nutrient composition tables were available: West Africa, Latin America, Southeast Asia, Northeast Asia, the United States, and India. For each of the 221 food items, these tables provide nutritient content of 18 essential nutrients and two nutrients of health concern (total fats and saturated fatty acids). We complemented the GENuS nutrient composition data sets with the nutritient content values for six additional essential nutrients (vitamin E, vitamin B12, vitamin K, manganese, selenium, and pantothenic acid) and two nutrients of health concern (sugar and cholesterol) from the USDA SR 28 nutrient composition table.34 This way we obtained the daily per capita intake of calories, 24 essential nutrients and four nutrients of health concern for all 152 countries. Dietary Environmental Footprint. In order to calculate the environmental footprint of national daily average diets, we match the recently available5,15 emission factors (i.e., environmental impacts per gram of food) to our product resolution (221 items).31 Emission factors are available for five environmental domains: greenhouse gas emissions (g CO2eq/g), freshwater use (liters/g), cropland use (m2/g), nitrogen application (gN/g) and phosphorus application (g P/g).5,15 We then multiply food emission factor with its daily average per capita intake levels and sum up to calculate national footprint for each of five environmental domains. Optimized Diets. For each of 152 countries, we use nonlinear optimization algorithm that minimizes the deviation from current diet (Δ) while meeting 38 constraints (Table 1) and calculate the optimized amounts of 221 food items ij Q opt, i − Q obs, i yz zz min Δ = ∑ jjjj zz j z Q opt, i Q obs, i i=1 k { 221

Table 1. Nutritional, Environmental, and Acceptability Constraints Applied in Nonlinear Optimization of National Diets Carried out in This Study constraint type nutritional constraints energy sugar saturated fats total fats cholesterol protein fiber vitamin C vitamin E calcium iron magnesium potassium thiamin riboflavin folate zinc vitamin B12 phosphorus copper manganese selenium niacin pantothenic acid vitamin B6 choline vitamin A vitamin K polyunsaturated fatty acids environmental constraints carbon emissions freshwater use land use nitrogen use phosphorus use acceptability constraints total weight individual foods alcohol, spices, stimulants items with zero intake

value 2300−3200 kcal/cap/day ≤125 g/cap/day ≤23 g/cap/day ≤65 g/cap/day ≤300 mg/cap/day ≥52 g/cap/day ≥29 g/cap/day ≥42 mg/cap/day ≥10 mg/cap/day ≥520 mg/cap/day ≥17 mg/cap/day ≥205 mg/cap/day ≥3247 mg/cap/day ≥1.1 mg/cap/day ≥1.1 mg/cap/day ≥364 μg/cap/day ≥6.1 mg/cap/day ≥2.2 μg/cap/day ≥757 mg/cap/day ≥0.8 mg/cap/day ≥2 mg/cap/day ≥55 μg/cap/day ≥14 mg/cap/day ≥4.7 mg/cap/day ≥1.2 mg/cap/day ≥550 mg/cap/day ≥544 RAE/cap/day ≥80 μg/cap/day ≥14 g/cap/day ≤1866 gCO2eq/cap/day ≤786 L/cap/day ≤5.01 m2/cap/day ≤27.4 gN/cap/day ≤6.35 gP/cap/day 80−120% of total weight of current diet >0.1 times and 30%) followed by China (∼20%) and Latin America (∼11%). In contrast, the footprints of the most low and lower middle income nations (Sub-Saharan Africa, South Asia, and India) increased by 10−20% from their current levels under the optimized diet due to addition of fruits, vegetables, and pulses to meet their daily nutrition and caloric goals (Figure 1). Interestingly, for many countries, the reductions varied across the five environmental domains reflecting trade-offs (Supporting Information Table S2). For example, in East Asia and Pacific, unlike the 10−20% reduction in other four footprints (Figure 1), the land footprint increases by 15% from the current levels (Figure 1c) under the optimized diet (although remaining below the planetary boundary). We also calculated the global aggregate environmental savings that will result if all countries adopted the optimized (sustainable) diet by multiplying the country-specific current and optimized environmental footprints (per capita per day; Supporting Information Table S2) with the respective population and taking the difference. Results show that this will reduce the global carbon emissions by 1.35Gt CO2eq/ year, bluewater consumption by 83.2 km3/year, nitrogen application by 7.8 Tg/year and phosphorus application by 1.41 Tg/year while keeping the global cropland use at almost the same as current levels. This corresponds to a 32% reduction in GHG emissions, 8% reduction in bluewater consumption, 12% reduction in nitrogen and 13% reduction in phosphorus

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RESULTS In terms of individual nutrients, we found that the current intake of eight out of 24 essential micronutrients (fiber, vitamin E, calcium, potassium, riboflavin, vitamin B12, choline and vitamin K) to be below the recommended levels for a number of countries. In the optimized diet, all of these eight nutrients increased to recommended values (Table 2; Supporting Information Table S1). Note that the optimized amounts of fiber, vitamin B12, vitamin E and saturated fats barely meet their recommended levels for most countries, meaning special efforts should be directed to increase their supply in global food systems. Importantly, unlike a flexitarian diet designed using the stylized approach,15 where the recommended levels of choline, riboflavin, fiber, calcium, vitamins (A, B12, E), and fats are not met for many countries, the optimized diet is able to meet the daily requirements of all nutrients for all countries (see cells marked in red in Supporting Information Table S1). In terms of individual environmental footprint, out of a total 152 countries, currently 85, 152, 148, 98, and 138 countries stay within food related per capita planetary boundary for carbon emissions, freshwater, cropland, nutrition, and phosphorus use, respectively. In contrast, under the optimized diet, all countries stay within all five planetary boundaries 7698

DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703

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Figure 2. Required changes in dietary behaviors to achieve sustainable diets. Percent departure from current diet calculated by taking the mean of the percentage difference in optimum intake amounts of each of 221 food items from their values in the current diet (Δdiet, c, eq 2, Materials and Methods). See Supporting Information Table S3,for all results.

Figure 3. Required changes in food intake. Difference between the optimum and current intake amounts of major food groups for nine World Bank regions in g capita−1day−1. FV is fruits and vegetables. Supporting Information Tables S4 and S5 present detailed results per food item per country.

sorghum), and moderate or slight increase in the intake of pulses, nuts, fruits, and vegetables (Supporting Information Tables S4 and S5). The lowest values for departure from current diet were found for certain Middle East and North African countries such as Iran, Turkey, and Israel (90−100%). This is because the dietary patterns of these countries are close to Mediterranean diets that are already high in fruits, vegetables, and pulses and low in environmentally intensive red meat and sugar with moderate amounts of fish, dairy, and poultry (Supporting Information Tables S4 and S5). The global median of departure values was 177%, while the departure score normalized with the global median (eq 3) varied from 25% (Iran) to 67% (Honduras). Overall, the optimized diet entails a reduction in intake of meat, dairy, rice, and sugar and an increase in intake of fruits, vegetables, pulses, nuts, and other grains in most countries (Figure 3; Supporting Information Table S4). Roots and tubers consumption needs to increase in all regions, especially in the Americas and China and excluding Africa where it is already at very high levels. Except for China, East Asia, and North America, the optimization results suggest a need to increase fish consumption in most countries. Supporting Information Table S4 shows the required change in intake amounts of each of 221 food items per country

application compared to current annual global levels. Note that these reduction estimates are conservative because we considered not all but only 152 countries for which data was available and also because we considered only production stage impacts and not the entire life cycle impacts of food items.5 These reduction estimates compare well with previous diet optimization studies.19−22 In terms of acceptability of optimized diet, the percent departure from current diet (Δdiet, eq 2, methods) is considerable for all countries, suggesting the need for a paradigm shift in the dietary behaviors across the globe (Figure 2; Supporting Information Table S3). Countries requiring highest departure from the current diets (>200%) to achieve sustainable diets are spread all over the globe (Honduras, El Salvador, Philippines, Sudan, USA, Mexico), albeit for different reasons. In Latin and North American countries, replacement of meat, dairy and eggs with roots, cereals, fruits, and vegetables, drives the departure while in African countries, a high departure value is due to increased caloric and intake amounts across all foods in general. For example, in India, the transition to sustainable diet entails 147% departure from the current diet requiring a high reduction in dairy, moderate reduction in rice and slight reduction in sugars and at the same time a high increase in the intake of other grains (e.g., barley, buckwheat, millet, oats, rye, 7699

DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703

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Second, regarding the nutritional constraints, we applied simple minimum recommended requirements, but nutrition is much more complex. For example, the bioavailability of protein and some minerals is higher from animal products than from plant sources.26,44 Further, presence of a food can affect the availability of nutrients in another food such as compounds in some plant-based foods inhibiting the absorption of nonheme iron and zinc.45,46 Therefore, a shift toward more plant-based diets may not satisfy physiological requirements even if total ingested quantity is above the recommended daily allowances (RDAs).47 Due to these factors, the optimized diet with reduced animal products carries risk of micronutrient deficiency, if not managed appropriately. Another limitation is that as our nutritional constraints (Table 1) we simply used the population-weighted average of the age and gender specific recommendations of the World Health Organization15 because we only had the mean food intake data for each country.31 To obtain more accurate results, the optimization should be performed on diets of each population group (age and sex groups, lactating, pregnant women, etc.) separately. Also, our algorithm satisfies the daily micronutrient requirements per country through changes in intake of food items alone. We did not incorporate the possibility that micronutrients recommendations can also be met through supplements or fortified fertilizers and food products. The latter option might be more environmentally efficient and also leave more room to keep the diets closer to current patterns and thus more culturally acceptable. Future studies should explore such options and the calculate the consequences for other dimensions of sustainability (e.g., economic, environment). We used the GENuS database that provides the food intake and nutrient composition for 221 food items per country31 and is of much higher resolution than the 94 aggregated food items in FAO’s food balance sheets (FBS).32 For example, the GENuS database provides intake amounts and nutrient composition separately for milk, cheese, ice cream as well as for grains and their flours or raw fruits and their juices. However, the data on actual food eaten (e.g., Pizza, burger, pasta, bread etc.) is not available yet. Therefore, the nutrition changes in many food items due to processing and cooking could not be taken into account in our analysis. Rather than the mean values, in a sensitivity run, we also ran the optimization algorithm considering the upper and lower limits of environmental planetary boundaries;5 however, this changed the optimized diet marginally and did not change the overall conclusions. Some past studies have used the recommended range of intakes for protein and fat as a percentage of dietary energy rather than maximum or minimum cut-offs (Table 1).21 As another sensitivity run, we thus reran the optimization algorithm using the range constraints for total fat (20 ≤ % energy from fat ≤35) and protein (10 ≤ % energy from protein ≤20) instead of max or minimum cut-offs on intake (total fats ≤65 g/cap/day and protein ≥52 g/cap/day). However, we found that the results change negligibly and the algorithm converges to a similar sustainable diet for all countries. Third, we could only consider the nutrition, environmental and acceptability dimensions of the sustainable diet in this study and were not able to account for economic, social and accessibility dimensions. The food and agriculture organization (FAO) of the United Nations define sustainable diets as the one that are “protective and respectful of biodiversity and

(33592 combinations), while Supporting Information Table S5 shows required changes for 20 broad food groups along with a color coding scheme to give an indication on how big of an increase or decrease in intake amounts is needed to achieve a sustainable diet in each country. While interpreting the required per capita food intake changes results (presented in Figure 3; Supporting Information Tables S4 and S5), it must be kept in mind that they do not tell the scale of the transition needed to achieve sustainable diets on a global scale due to huge differences between the population of different countries. However, broadly speaking, it can be seen that a large proportion of world’s population need to increase fruits, vegetables, and roots consumption and decrease dairy and meat consumption (Figure 3).

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DISCUSSION This study is the first to derive country-specific diets that meet several cultural acceptability criteria while at the same time meeting minimum nutrient requirements and the per capita food related planetary boundaries using a nonlinear diet optimization algorithm. Starting with the current daily average diet of 152 countries, optimization results show that each country requires unique changes in their current dietary behavior in order to achieve a nutritional and environmentally sustainable diet. Importantly, we found that unlike the nationspecific flexitarian diet designed using the previous stylized approaches,15 the optimized diet is able to meet the daily requirements of choline, riboflavin, fiber, calcium, and vitamins for all countries. The country and food-specific changes produced for this study (Supporting Information Tables S4 and S5) can provide useful insights for policy-makers in designing necessary interventions to shift the national dietary behaviors toward sustainable diets. Our nutrition and environmental analysis revealed that the daily recommended values for fiber, vitamin B12, vitamin E, and saturated fats and the planetary boundaries for carbon emissions and nitrogen application were most difficult to meet, implying that they need special attention (Supporting Information Tables S1 and S2). Despite using the latest available input data, our results come with several uncertainties and limitations that should be considered when interpreting the results. First, we could not include other food-related environmental impacts such as biodiversity loss,36−42 industrial pollution, disease risk, etc. Further, owing to data unavailability, we simply use the available global average values of environmental emission factors for different food items and could not employ countryspecific values that account for variability in the production methods.5,15 A recent review showed that the environmental impact can vary over 50-fold among producers of the same product depending upon the production system or region.43 The environmental planetary boundaries that we use (based on the work of Springmann et al.5) are global average values with inherent limitations and ideally should be derived separately for different regions taking into account local climatic, geographical, human, and other factors (e.g., limits on annual water use would be very different in water scarce regions of India or Middle East compared with Western Europe). Overall, we could not calculate the uncertainty around our results because the input data on intake amounts,31 nutrition composition,31 and environmental emission factors of food items5 that we use do not provide the 95% confidence intervals. 7700

DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703

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We found that in many high-income countries, achieving an optimized diet entails a strong reduction in meat and dairy intake in order to meet the environmental goals. As shown by previous public surveys, such shifts might not be acceptable to certain population groups due to their social, personal, and cultural values.17 In general, consumers are less likely to change their food preferences for health or environmental benefits.49,50 In the US, Canada, Europe, or even China, there is very large infrastructure devoted to providing meat or animal-sourced protein, and there will be significant economic and political resistance from this sector to a dietary shift toward plant-based proteins. To address these barriers, policy makers need to design interventions or incentives aimed at favoring the adoption of sustainable diet by consumers in real life considering multiple factors such as price concerns, product availability and accessibility, consumer understanding, purchasing habits, personal benefits, physical microenvironment etc.51−54 Regarding influencing consumer behavior toward less meat eating, a recent review presented encouraging evidence that interventions providing access to meat alternatives, changing the sensory properties (e.g., visual presentation) of meat and meat alternatives at point of purchase, and reducing portion sizes of meat servings offered the most promise.55 To complement the efforts to influence consumer behavior, a large number of other synergistic strategies would need to be implemented in order to increase the feasibility and speed of transitions to sustainable diets. These include, but are not limited to, reduction in food waste and losses12 and improving the agricultural production practices2 to reduce the environmental footprint of food systems; increasing agriculture diversity and replacing high-yield cereals with nutrient dense cereals;56 and leveraging the potential of dietary supplements,57 biofortification,58 emerging technologies for synthetic meat,59 algae,60 edible insects,61 sustainable aquaculture production,62 innovative food reformulations,63 etc. Addressing the above research gaps, gathering data on region-specific acceptability constraints, and incorporating them into the optimization algorithm and reducing the inherent uncertainties in the underlying food intake,31 nutrient composition,31 and environmental footprint5,15 data represent important future research fronts. The analysis demonstrates that nonlinear optimization is a powerful tool to design sustainable diets under multiple constraints.

ecosystems, culturally acceptable, accessible, economically fair, and affordable; nutritionally adequate, safe and healthy; while optimizing natural and human resources”.18,19 A shift from one food group to the other might be too expensive for majority of population or simply not feasible due to accessibility/ availability/social issues (e.g., low production and imports of a particular food group) especially in low-income countries and therefore can constrain the adoption of the optimized diets.48 For example, a dietary shift toward increased fish consumption need to consider whether there are sufficient global wild-fish stocks to meet these recommendations for the whole population.23 We found that under the optimized diet, the per capita cropland use footprint increases by over 15% in several countries (Figure 1c) but our algorithm does not account for the possibility that such an expansion of cropland or an increase in imports might not be feasible in certain countries due to geographical or economic constraints (although most of these African and Asian countries have substantial yield gaps and food losses that if managed can circumvent the need for cropland expansion domestically or abroad).2 Future studies should include additional countryspecific economic, feasibility and accessibility constraints in the optimization problem to achieve more realistic diets. Fourth, although cultural acceptability was taken into account it cannot guarantee that the modeled shift would indeed be acceptable to the population. One limitation is the broad geographical scale of our study as we obtain the average sustainable diet at the broad country level (Supporting Information Table S4). This is because a more detailed food intake and other data at subnational or local levels is not readily available for all countries. Caution must be taken to generalize our findings for all regions or population groups within a country. It might be that some of our country average results might be at a conflict with the local context. For example, for India, our algorithm predicts a need for decrease in rice consumption by over 100 g per capita per day and an increase in wheat intake by ∼80 g (Supporting Information Table S5). However, this might not be acceptable or feasible in South India, where rice is the major staple food, in contrast with the North, where wheat is the major staple. Such conflicts between country average and local context would only arise for large countries with a high diversity of food culture or climate conditions, etc. For small or homogeneous countries, the calculated dietary shifts should be mostly valid. Still, the country average results have a value because it is the cumulative impact of the food consumption of all countries, wich will decide the fate of global environmental planetary boundaries and global food related sustainable development goals (SDGs). Regardless, if the local or even individual level food intake and constraints data is available, the optimization algorithm can be run to obtain the corresponding sustainable diet. Our use of a simple objective function (eq 1) and the four acceptability constraints (Table 1) do not entirely address the possibility that what constitutes a major part of one’s diet (e.g., rice in South East Asia) is typically, but not always, more objectionable than changes in less prominent parts of the diet. Also, in a country, some specific food items are culturally much more important than others, and this is not necessarily reflected in the consumed amounts (e.g., garlic). Employing constraints and objective function that take into account the country-specific preferences for different food items would deliver much higher culturally acceptable optimized diets.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.8b06923.

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Daily per capita intake amounts of all nutrients per country; environmental footprints per country; required percent departure from current diets per country; food item and food group intake changes required per country under an optimized diet (XLSX)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +91 512 259 2087. Fax: +91 512 259 7395. ORCID

Abhishek Chaudhary: 0000-0002-6602-7279 7701

DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703

Article

Environmental Science & Technology Author Contributions

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A.C. conceived the idea, designed the study, compiled input data, analyzed results, and wrote the manuscript. V.K. implemented nonlinear optimization algorithm, analyzed results, plotted graphs, and contributed ideas. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS A.C. acknowledges funding from the Initiation Grant of IIT Kanpur, India (project number 2018386).

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DOI: 10.1021/acs.est.8b06923 Environ. Sci. Technol. 2019, 53, 7694−7703