Abstract
Food production is a major driver of greenhouse gas (GHG) emissions, water and land use, and dietary risk factors are contributors to non-communicable diseases. Shifts in dietary patterns can therefore potentially provide benefits for both the environment and health. However, there is uncertainty about the magnitude of these impacts, and the dietary changes necessary to achieve them. We systematically review the evidence on changes in GHG emissions, land use, and water use, from shifting current dietary intakes to environmentally sustainable dietary patterns. We find 14 common sustainable dietary patterns across reviewed studies, with reductions as high as 70–80% of GHG emissions and land use, and 50% of water use (with medians of about 20–30% for these indicators across all studies) possible by adopting sustainable dietary patterns. Reductions in environmental footprints were generally proportional to the magnitude of animal-based food restriction. Dietary shifts also yielded modest benefits in all-cause mortality risk. Our review reveals that environmental and health benefits are possible by shifting current Western diets to a variety of more sustainable dietary patterns.
Generated Summary
This research presents a systematic review assessing the impacts of shifting dietary patterns on greenhouse gas (GHG) emissions, land use, water use, and health. The study reviewed evidence on changes in these indicators resulting from a transition from current dietary intakes to environmentally sustainable dietary patterns. The review included 63 studies and 210 scenarios. The methodology followed PRISMA guidelines, and the environmental impacts considered were GHG emissions, land use, and water use. The review primarily focuses on studies that quantified changes in GHG emissions, land use, or water use between average population-level dietary intake and proposed sustainable dietary patterns. The included studies used dietary or consumer expenditure surveys or food balance sheets to inform the baseline diets, with the baseline dietary data from 1995 onwards. The study aimed to substantially expand on previous reviews and included grey literature while also considering the health impact of various sustainable dietary patterns. The analysis involved assessing the relative differences in environmental impacts between baseline and sustainable diets, with medians used to compare the various sustainable dietary patterns.
Key Findings & Statistics
- The median changes in GHG emissions across all sustainable diet types were -22%.
- The median changes in land use were -28%.
- The median changes in water use, across all sustainable diet types, were -18%.
- The largest environmental benefits across indicators were seen in those diets which most reduced the amount of animal-based foods, such as vegan (first place in terms of benefits for two environmental indicators), vegetarian (first place for one indicator), and pescatarian (second and third place for two indicators).
- Vegan diets had the greatest median reductions for GHG emissions (-45%) and land use (-51%).
- Vegetarian diets had the largest benefit for water use (median -37%).
- 197 scenarios showed a reduction in environmental impacts when switching from baseline to alternative dietary patterns (sign test: p<0.0001).
- Thirteen scenarios showed an increase or no impact.
- 14 sustainable dietary patterns were proposed: vegetarian, vegan, pescatarian, replacing ruminant with monogastric meat, balanced energy intake, following healthy guidelines, Mediterranean diet, New Nordic diet, and meat reduction, with other sub-scenarios.
- The health effects of adopting sustainable diets were limited, with 11 out of the 14 sustainable diet types being modeled.
- All studies showed positive health effects, ranging from less than 1% reduction in estimated mortality risk for vegetarian diets, to 19% for vegan diets.
Other Important Findings
- The study found that reductions above 70% of GHG emissions and land use, and 50% of water use, could be achieved by shifting typical Western diets to more environmentally sustainable dietary patterns.
- Medians of these impacts across all studies suggest possible reductions of between 20-30%.
- The ranking of sustainable diet types showed similar trends for land use and GHG emissions.
- The study highlights that the largest environmental benefits are linked to diets that significantly reduce animal-based foods.
- Environmental data in the studies (where shown) on the land use, GHG emissions, and water use impacts from the production of food items showed decreasing impacts.
- There was no statistical association between the magnitude of environmental and health benefits.
- The study mentions that the impacts of sustainable diets are linked to a number of SDGs, including goals on sustainable agricultural practices, health, water use, and climate change.
Limitations Noted in the Document
- The available studies were from a narrow range of high-income countries with different baseline dietary patterns and used largely high-income country specific environmental data sources. The results may therefore only be generalizable to high-income countries.
- The data on environmental impacts did not provide measures of variance.
- The study was limited to graphical and non-parametric statistical methods to assess the differences between sustainable dietary patterns.
- The study was unable to rule out any effects of publication bias in the literature.
- The use of environmental indicators varied across studies, such as whether blue, green, or grey water (or a combination) was used, and whether GHG emissions included the often significant emissions from land use change.
- The study used relative differences in the analysis to accommodate differences in methodology across studies.
- The reviewed diets cannot be designated sustainable in an absolute sense, as this will depend on population growth, evidence about planetary boundaries, and assumptions about other environmental trends.
Conclusion
The systematic review concludes that a shift towards more sustainable dietary patterns can significantly reduce environmental impacts, particularly in high-income countries. Reductions in GHG emissions and land use were largely proportional to the magnitude of meat and dairy reduction, with vegan and vegetarian diets showing the greatest benefits. The study suggests that by shifting typical Western diets to more sustainable dietary patterns, reductions above 70% of GHG emissions and land use, and 50% of water use could be achieved. The median impacts across all studies suggest possible reductions of between 20-30%. The review highlights the importance of reducing animal-based foods to achieve these goals. While there is potential for health benefits through these dietary shifts, the study notes the need for further research on regional and food-specific environmental impacts, including for fisheries and aquaculture, as well as measures of variance. The review emphasizes that promotion and uptake of these diets could offer a route, along with other strategies, to achieving several of the SDGs. The researchers emphasize the importance of a redoubling of efforts to promote the uptake of diets that support these changes, which could bring environmental and health benefits. Overall, the review underlines that environmentally sustainable eating should consider dietary requirements of sub-population groups, and shifts to sustainable diets must be affordable and desirable for consumers. The study supports the conclusions of previous reviews and expands on them by including a larger number of studies and dietary patterns, including grey literature, and by using multiple environmental indicators.
IFFS Team Summary
- Compares Vegan, lacto veg, pescatarian, meat reduction, and omnivore diets
- The greater the decrease in animal products, the better the impact on GHG, Land use and Water footprint
- Vegan diet resulted in the greatest decrease in all-cause mortality – 19% decrease
- article also listed in Environment and Food Security List
- Article was used as a reference for the 2017 Canada food guide process