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 systematic review investigates the environmental and health impacts of shifting current dietary intakes to environmentally sustainable dietary patterns. The study systematically reviewed evidence on changes in greenhouse gas (GHG) emissions, land use, and water use from shifting current dietary intakes to environmentally sustainable dietary patterns. Fourteen common sustainable dietary patterns were identified across reviewed studies. The analysis aimed to expand on previous reviews and included grey literature, along with additional indicators of water use and health impacts. The review followed PRISMA guidelines, searching databases such as Scopus, ProQuest, PubMed, Web of Science, and Science Direct. Inclusion criteria involved quantifying changes in GHG emissions, land use, or water use between average population-level dietary intake and proposed sustainable dietary patterns. The environmental impacts considered were GHG emissions, land use, and water use, and included a quality assessment that considered the source and methods of environmental impact data used. Study quality was assessed, and analyses were performed using STATA version 14.
Key Findings & Statistics
- A total of 210 scenarios were extracted from 63 studies. Of these, 204 scenarios were modeled on national-level diets in HICs.
- Fourteen sustainable dietary patterns were proposed, including vegetarian, vegan, pescatarian, replacing ruminant with monogastric meat, balanced energy intake, following healthy guidelines, Mediterranean diet, New Nordic diet, and meat reduction.
- The median changes in GHG emissions, land use, and water use, across all sustainable diet types, were -22%, -28%, and -18%, respectively.
- 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).
- The ranking of sustainable diet types showed similar trends for land use and GHG emissions, with vegan diets having the greatest median reductions for both indicators (-45% and -51%, respectively).
- The scenarios of balanced energy intake or meat partly replaced with dairy, having the least benefit.
- The seven studies reporting health effects of adopting sustainable diets, 11 out of the 14 sustainable diet types were 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
- Of the 210 scenarios, 197 showed a reduction in environmental impacts when switching from baseline to alternative dietary patterns (sign test: p<0.0001), while thirteen scenarios showed an increase or no impact.
- The ranking of sustainable diet types showed similar trends for land use and GHG emissions, with vegan diets having the greatest median reductions for both indicators (-45% and -51%, respectively), and scenarios of balanced energy intake or meat partly replaced with dairy, having the least benefit.
- The magnitude of health effects across the sustainable dietary patterns did not show a statistical association with that of environmental benefit.
- Fourteen studies came from grey literature.
Limitations Noted in the Document
- The available studies were from a narrow range of HICs with different baseline dietary patterns, and used largely HIC-specific environmental data sources. The results may therefore only be generalizable to HICs.
- The data on environmental impacts did not provide measures of variance, and we were limited to graphical and non-parametric statistical methods to assess the differences between sustainable dietary patterns.
- 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.
Conclusion
The review reveals 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%. This review is the most recent and comprehensive to date, and the first to compare impacts across GHG emissions, land use, and water use. The study’s findings support previous reviews in this area which also pointed to the potential for reductions in GHG emissions and land use from dietary change. The use of multiple environmental indicators also highlights possible trade-offs across the proposed dietary patterns, both in magnitude and direction of the environmental impacts. The results suggest that environmental benefits are largely proportional to the magnitude of meat (particularly from ruminants) and dairy reduction. The promotion and uptake of diets that support these changes could bring environmental and health benefits. The results also suggest that, complete removal of animal-source foods is not realistic in many cultures and may have important health implications, and that meat and dairy are high-quality sources of protein and micronutrients, and ensuring adequate bioavailable supply of these is essential for public health.
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