Characterization of Average and Recommended Diets.

In general, NRDs are specific to the health challenges from diets found in that nation. For example, India focuses on increasing caloric and nutritional content (21), whereas the United States focuses on reducing caloric intake (22). Compared with average national diets, NRDs generally recommend a substantial reduction in sugars, oils, meat, and dairy (Fig. 1 and Figs. S2–S4). These reductions are largest in high-income nations, where fruit, vegetables, and nuts are generally recommended for replacement calories. These changes are very large and would require significant departures from current dietary patterns. It is likely that any shifts to these recommended diets would occur gradually. These general trends are similar for upper-middle–income nations but with less reduction in meat and several nations recommending replacement calories from dairy. India and Indonesia, both lower-middle–income nations, are the only nations with recommendations for increases in meat intake. This may be partly due to the relatively high prevalence of undernutrition and micronutrient deficiencies in these regions.

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Fig. 1.

Overview of the composition of energy intake by food category per person per day for national average diets, national recommended diets, and the difference between them, for all countries in this study. Notice that NRDs have been scaled so that total calorie intake matches that of the average diet (isocaloric approach). Although the proportion of grains for Hungary, Latvia, and Portugal may seem large, these are the recommendations (Supporting Information).

However, even in these cases the increase is small, and replacement calories from fruit, vegetables, and nuts are recommended, as in the case for high-income nations. In general, there is very little change in the consumption of fish in all nations, with high-income nations recommending a small reduction and middle-income nations recommending a moderate increase. Some eastern European nations have recommended diets showing very little change with respect to the average diet; this may be partially due to the fact that these guidelines have not been updated for some time and partly due to continuing concerns of undernutrition in some sectors (i.e., rural communities) of those societies (23, 24).

In average diets, the most important source of energy is grains, which is greater in middle-income nations than in high-income nations (Fig. S1). The second biggest source of energy is dairy, which is higher in high-income nations compared with middle-income nations (Fig. S1). Fats compose less dietary energy in middle-income nations compared with high-income nations (Fig. S1). This is also true for protein intake but is less pronounced. The relative contribution of protein to overall energy intake varies between 10 and 15% of the total energy. Meat and dairy are the most important contributors to protein intake in most nations except for Turkey, South Africa, Indonesia, India, and China. In all nations, the contribution of fat is mainly from dairy and other foods (i.e., oils).

Environmental Impacts of Average Diets.

The greenhouse gas (GHG) emission impacts for average diets significantly increase with income, from 1.1 kg CO₂ eq per person per day (p⁻¹⋅d⁻¹) in lower-middle–income nations to 1.6 CO₂ eq⋅p⁻¹⋅d⁻¹ for upper-middle–income nations and 2.4 kg CO₂ eq⋅p⁻¹⋅d⁻¹ for high-income nations (Fig. 2A). Animal products (meat, fish, and dairy) account for 22%, 65%, and 70% of emissions in the diets of lower-middle–, upper-middle–, and high-income nations, respectively. Some nations show very different impacts to counterparts within the same group, with Brazil and Australia having emissions over 200% higher than the average of their respective income groups and driven by meat consumption. This is likely due to both the amount of meat in the diet and the preponderance of grass-fed beef within both of these regions, associated with higher methane emissions than grain-fed beef (25). Although not as extreme, the United States, Canada, and Norway have emissions 40% higher than the average of their income group, with meat, dairy, and fish contributing larger amounts than the average, respectively. In the United States and Canada this is also likely due to grass-fed cattle; in Norway, fishing contributes more than in other regions, due to both demand and fuel-intensive fleets (26).

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Fig. 2.

(A) Absolute environmental impacts of average diets for different national income groups per person. (B) Differences in environmental impacts between average and recommended diets per person. Net change and change by food group are shown. Both panels give GHG and eutrophication emissions in terms of per day and land use in ongoing, yearly requirement. Land use in Australia has been truncated in both panels for ease of visualization (in A, total Australian land use is 3.3 ha; in B the change is a reduction of 1.0 ha).

In general, eutrophication impacts follow a similar pattern as GHG impacts, increasing from 13.1 kg PO43− eq⋅p⁻¹⋅d⁻¹ in lower-middle–income nations, to 32.5 kg PO43− eq⋅p⁻¹⋅d⁻¹ for upper-middle–income nations, then down slightly to 32.1 kg PO43− eq⋅p⁻¹⋅d⁻¹ for high-income nations. The increases in eutrophication impacts due to animal products in Brazil, Australia, Canada, and the United States are larger than those for GHGs, with 121, 119, 57, and 59 kg PO43− eq⋅p⁻¹⋅d⁻¹, respectively. Again, this is likely due to the preference for extensive grass grazing of cattle in these regions compared with other nations.

Average land use also follows similar patterns to those of emissions but with a smaller difference between lower-middle– and upper-middle–income nations, varying between 0.11 ha⋅p⁻¹ for lower-income nations, 0.29 ha⋅p⁻¹ for middle-income nations, and 0.39 ha⋅p⁻¹ for high-income nations. The average land use in high-income nations was over 3.5 times that of the low-middle–income average.

The absolute estimates of the environmental impacts of estimated average diets reported in the current study are in the same order of magnitude, but slightly lower, than those within the LCA literature more generally (6). One reason for these differences arises from the fact that here we consider foods in diets only and omit emissions from cooking, preparation, and waste. Other factors that can lead to discrepancies between input–output analyses and LCA results are differences in allocation and aggregation (27, 28).

Environmental Impacts of Shifting to Nationally Recommended Diets.

Environmental impacts of shifting from average to nationally recommended diets vary across nations and income groups (Figs. 2B and 3). High-income nations see the greatest reduction in impacts due to dietary shifts, with an average reduction of 0.34 kg CO₂ eq⋅p⁻¹⋅d⁻¹ (−13.0%), 4.7 kg PO43− eq⋅p⁻¹⋅d⁻¹ (−9.8%), and 0.07 ha⋅p⁻¹ (−5.7%). If shifts in caloric intake are also considered, these reductions increase to 0.63 kg CO₂ eq⋅p⁻¹⋅d⁻¹ (−24.7%), 8.3 kg PO43− eq⋅p⁻¹⋅d⁻¹ (−21.3%), and 0.1 ha⋅p⁻¹ (−17.6%) (see Fig. S4 for more information). In middle-income nations, marginal reductions are observed, with changes of 0.01 kg CO₂ eq⋅p⁻¹⋅d⁻¹ (4.4%), 2.0 kg PO43− eq⋅p⁻¹⋅d⁻¹ (1.1%), and 0.02 ha⋅p⁻¹ (−2.3%). Isolating to upper-middle–income nations only by omitting the different trends in the two lower-middle–income nations, India and Indonesia, gives average reductions of 0.04 kg CO₂ eq⋅p⁻¹⋅d⁻¹ (−0.8%), 3.8 kg PO43−eq⋅p⁻¹⋅d⁻¹ (−7.7%), and 0.03 ha⋅p⁻¹ (−7.2%). Large-scale adoption of NRDs implies increases in impacts from lower-middle–income nations and decreases in other income categories. The net result of following NRDs for the countries examined here results in reductions of 0.19 Gt CO₂ eq⋅a⁻¹ and 4.32 Gt PO43− eq⋅a⁻¹ in an isocaloric estimate and 0.53 Gt CO₂ eq⋅a⁻¹ and 10.6 Gt PO43− eq⋅a⁻¹ in a nonisocaloric estimate.

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Fig. 3.

Relative differences in environmental impacts between nationally recommended and average diets for high-income and lower-income nations. Red line indicates median relative difference; left and right box limits show first and third quartiles, respectively; whiskers show range from minimum to maximum; and blue crosses show the mean, population-weighted impact.

Exceptions to trends in high-income nations, showing larger (>0.1 kg CO₂ eq⋅p⁻¹⋅d⁻¹) increases in environmental impacts associated with NRDs, are Poland, South Korea, and Switzerland. In all cases, this is partially due to increasing amounts of vegetables, fruits, and nuts. In Switzerland, vegetables, fruits, and nuts make up the total increase and may be due to the use of greenhouses and heating oil in particular (29). In Poland and South Korea, higher recommendations for dairy also contribute to increasing environmental impacts. In middle-income nations, clear exceptions are Brazil and South Africa. In Brazil, large reductions are from meat and dairy, as discussed above. The increases in South Africa relative to other nations in the income group are due to dairy and increased vegetables, fruits, and nuts. South Africa has historically suffered from a high prevalence of undernutrition but, after several decades of transition, now has a high rate of obesity due to a shift to a diet high in fat, simple sugars, and animal-based foods (30). However, the South African NRD suggests even greater intake of dairy products, which may indicate that the advice has failed to keep up with developing dietary changes among some sections of the population, especially among the urban population. The advice may still be appropriate for the rural poor where undernutrition and micronutrient deficiencies are common. In lower-middle–income nations, India and Indonesia, impacts from following recommended diets are associated with an increase in impacts of 0.1 kg CO₂ eq⋅p⁻¹⋅d⁻¹ (+17.0%), 4.0 kg PO43− eq⋅p⁻¹⋅d⁻¹ (32.0%), and 0.02 ha⋅p⁻¹ (14.8%). This is predominately driven by increased meat and fish intake. These increases move the absolute impacts of NRDs in lower-middle–income nations closer to those in high-income nations. If both income groups adopted NRDs over current average diets, lower-middle–income diets move from 47% of the GHG impact of high-income diets to 67.4%.

In terms of food groups, changes in meat and dairy intake would result in a significant reduction in GHG emission, eutrophication, and land use in all countries except three lower-income nations, India, Indonesia, and Romania. Changes in the intake of vegetables, fruits, and nuts will result in an increase in GHGs emission, eutrophication, and land use for all countries except Greece and The Netherlands (Fig. 2B). In some specific cases, such as the United States and Australia, significant reductions also arise from limiting fats and sugars.

Trade Impacts.

Trade-linked data allow for a further investigation of embodied environmental impacts in imports of foods related to average and recommended diets. In general, for average diets, the largest global food producers and exporters show the lowest imports of embodied GHGs, for example, the United States, Brazil, Europe, and Australia. In contrast, Japan, Russia, and Canada show large imports of embodied GHGs. Diets associated with NRDs increase import dependence in Australia and Canada while reducing import dependence significantly in Japan, and less so in Brazil, South Africa, India, and Russia (Figs. S7–S9).

Further Opportunities in NRDs.

The environmental impacts of NRDs vary widely among nations because their emphasis is driven by local dietary concerns (Fig. 2B and Fig. S2). Many middle-income nations have greater recommended meat intake than high-income nations, likely due to the relatively high prevalence of protein energy malnutrition and widespread micronutrient malnutrition, especially where large-scale food fortification programs have limited reach. These recommendations could be improved from an environmental perspective by advising the substitution of meat-based with plant-based proteins, such as legumes and nuts, as has been done in most high-income nations. Some nations recommend a reduction of red meat specifically or substitution with white meat for health reasons (31). Although this does align with environmental outcomes by reducing ruminant consumption, this still may lead to a relatively high (lean or white) meat intake, which has still disproportionate environmental impacts compared with other food types (32). Here we have focused on an isocaloric analysis whereby NRDs are altered such that the proportion of the different food categories matches that of the original NRD, but the overall caloric intake is scaled so that it matches that of the current average diet (Materials and Methods). An alternative way to harmonize the NRDs would be to scale the caloric intake not to a country-specific average but to the caloric intake recommended by global guidelines of ∼2,200 kcal⋅p⁻¹⋅d⁻¹ (33). National recommended diets average around that same value; thus, such an analysis would be very close to the analysis of the nonisocaloric NRD (Fig. S4).

As this work shows, different issues and thus impacts are prevalent around the world depending on income. For example, further impact mitigation in high-income nations may be achieved by lowering the recommendations for dairy, which remains an important contributor of GHG emissions in many nations even under recommendation-compliant diets. However, although partial replacement of meat and dairy by plant-derived food sources does not substantially change the adequacy of nutrient intake (34, 35), the extent to which this can be applied in NRDs and then extrapolated globally needs to be established. Furthermore, in high-income nations, countries with high fish intake (Mediterranean and Scandinavia) show large reductions in land use relative to other nations. A high intake of fish is increasingly popular in new recommendations for nutritional reasons, but amounts may be lowered while still aligning desired health outcomes (36) with concerns about biodiversity loss in food marine webs (37). Several studies have shown that dietary quality varies not only between nations but also regionally within countries, for example, by socioeconomic background (38), ethnic background (39, 40), or rural vs. urban areas (41). Further research based on individual dietary data globally is needed to translate our results within countries, such as for specific subgroups, especially disadvantaged groups.

Overall, our results show that in many cases, there are environmental impact benefits to adopting NRDs. At present these benefits are smaller than other interventions in the environmental impact of food systems such as reductions in food waste (42). Further benefits from NRDs could be derived by incorporating sustainability further into the recommendations. In general, in high-income nations, a reduction in the recommended intake of (nonred) meat, dairy, and fish products would be beneficial on both accounts. NRDs for lower-middle– and upper-middle–income nations will also have to be adapted quickly as those countries develop and experience shifts in average diets. These shifts will have to be cognizant of the continuing challenges of the double burden of malnutrition. Although some countries have incorporated recommendations related to sustainable diets, implementing actual sustainable dietary guidelines remains challenging. For example, the 2016 Dietary Guidelines for Americans recommend increasing fruit and vegetable consumption, but current national production is insufficient to accommodate the adoption of this specific guideline by the majority of US citizens (43). In addition, there are tensions between the environmental and health impacts of fruit and vegetables grown in greenhouses or in countries where unseasonal production is high, such as in the United Kingdom (44). As a result, it will likely be necessary to tailor sustainable dietary recommendations to regional and cultural circumstances. This principle has been successfully applied in the new Nordic dietary recommendations and the Mediterranean diet (45). The work presented here will help policy makers quantify and optimize NRDs from an environmental perspective, building on the current knowledge of sustainable diets, which is important because consumers on their own are more likely to follow dietary guidelines developed with a health outcome in mind, rather than an environmental one (46).