Abstract
The Food and Agriculture Organization defines sustainable diets as nutritionally adequate, safe, healthy, culturally acceptable, economically affordable diets that have little environmental impact. This review summarizes the studies assessing, at the individual level, both the environmental impact and the nutritional quality or healthiness of self-selected diets. Reductions in meat consumption and energy intake were identified as primary factors for reducing diet-related greenhouse gas emissions. The choice of foods to replace meat, however, was crucial, with some isocaloric substitutions possibly increasing total diet greenhouse gas emissions. Moreover, nutritional adequacy was rarely or only partially assessed, thereby compromising the assessment of diet sustainability. Furthermore, high nutritional quality was not necessarily associated with affordability or lower environmental impact. Hence, when identifying sustainable diets, each dimension needs to be assessed by relevant indicators. Finally, some nonvegetarian self-selected diets consumed by a substantial fraction of the population showed good compatibility with the nutritional, environmental, affordability, and acceptability dimensions. Altogether, the reviewed studies revealed the scarcity of standardized nationally representative data for food prices and environmental indicators and suggest that diet sustainability might be increased without drastic dietary changes.
Generated Summary
This review article examines epidemiological studies on the environmental impact of diets, focusing on how food choices influence diet sustainability. The research approach involves analyzing existing studies that assess the environmental impact and nutritional quality of self-selected diets at the individual level. The methodology includes categorizing studies based on their aims, such as identifying dietary contributors to environmental impacts and simulating the effects of dietary changes. The scope of the review covers various aspects of diet sustainability, including greenhouse gas emissions, nutritional adequacy, affordability, and cultural acceptability. The goal is to identify strategies to improve diet sustainability through changes in food choices, emphasizing the role of meat consumption and the importance of considering all dimensions of sustainability.
Key Findings & Statistics
- The Food and Agriculture Organization attributed 14.5% of all human-induced GHGEs to the livestock sector.
- Aston et al. identified a dietary pattern low in red and processed meat that was already followed by a substantial fraction of the UK population.
- In a study based on dietary intake of 1724 adults, diet-related GHGEs were reduced by 0.47 kg of CO2e per person per day (12%).
- The study estimated reductions in health risk were 9.7% and 6.4% for coronary heart disease, 12% for diabetes, and 12.2% and 7.7% for colorectal cancer.
- Temme et al. found that meat was identified as the most important contributor to diet-related land use in this population (contributing 39% to land use).
- Temme et al. also found that when all meat and dairy foods were replaced by plant-based products, land use was halved and estimated saturated fatty acids intake decreased by 4% of total energy.
- Temme et al. found that meat and cheese contributed about 40% and drinks (including milk and alcoholic beverages) 20% to daily GHGEs.
- Biesbroek et al. found that total meat intake, which represented 3.6% of daily weight intake (and 11% of daily energy intake), was identified as the main contributor to environmental impact by accounting for approximately 30% of both dietary GHGEs and land use.
- The Vieux et al. study found that the meat and deli meat food group was the strongest contributor to diet-associated GHGEs: its mean contribution to emissions (27%) was more than twice as high as that generated by other food groups.
- The mean value for diet-related GHGEs was 4170 g (SD, 1162 g) of CO2e per day.
- Meat reduction induced mean decreases of 35 kcal/d and 4.1% of diet-related GHGEs in scenario 3 (20% reduction in meat and/or deli meat intake) and mean reductions of 133 kcal/d and 12% of diet-related GHGEs in scenario 4 (meat reduction to reach 50 g/d maximum and removal of deli meat).
- Scarborough et al. found that the age-, sex-, and energy-adjusted mean GHGEs (in kg of CO2e/2000 kcal) were 7.19 for high meat-eaters (≥100 g/d), 5.63 for medium meat-eaters (50–99 g/d), 4.67 for low meat-eaters (<50 g/d), 3.91 for fish-eaters, 3.81 for vegetarians, and 2.89 for vegans.
- Soret et al. found that moving from the nonvegetarian to the semivegetarian diet equates to a difference of 25 g of ground beef per day.
- Monsivais et al. found that adults in the highest quintile of the DASH accordance scores consumed diets with GHGEs 16% lower (-1.1 kg of CO2e/d) but 18% more costly (+£0.67/d) than adults in the lowest quintile.
Other Important Findings
- The choice of foods to replace meat is crucial, as some substitutions may increase greenhouse gas emissions (GHGEs).
- High nutritional quality is not always associated with affordability or lower environmental impact.
- Nonvegetarian self-selected diets in the population show good compatibility with nutritional, environmental, affordability, and acceptability dimensions.
- The studies reveal a scarcity of standardized data for food prices and environmental indicators, suggesting diet sustainability can be increased without drastic dietary changes.
- The review highlights the importance of considering all dimensions of diet sustainability (nutritional adequacy, health impact, affordability, cultural acceptability, and environmental footprints).
- Reductions in meat consumption and energy intake are key factors in reducing diet-related GHGEs.
- Studies indicate that diet sustainability might be increased without drastic dietary changes.
- The study also noted that the main factor to reduce diet-related GHGEs is the reduction of meat consumption.
- A modeling approach to quantify the risks of coronary heart disease, diabetes, and colorectal cancer was used.
- The studies suggest that reducing energy intakes, especially from animal-based foods and sugar- and alcohol-containing drinks, will help reduce the environmental impact of diets.
- In the analysis based on food consumption data, the meat and deli meat food group was the strongest contributor to diet-associated GHGEs.
- Meat and deli meat food group was the strongest contributor to diet-associated GHGEs.
- The authors also observed significant trends toward lower consumption of total fat, saturated fat, and protein and higher consumption of carbohydrate, total sugar, fiber, and fruit and vegetables as the quantity of animal-based products in the diet decreased.
- Studies suggest that a large proportion of the population is not yet ready to consume a fully plant-based diet.
- The review emphasizes that increasing diet sustainability does not require drastic or unrealistic food changes.
Limitations Noted in the Document
- Nutritional adequacy was often not fully assessed, potentially compromising the assessment of diet sustainability.
- High nutritional quality was not necessarily associated with affordability or lower environmental impact.
- A lack of accurate data limited the evaluation of the impact of the source and the production mode of the plant food substitutes.
- The study did not consider the impact of choosing a specific food production mode or source.
- The studies used a compilation of published environmental data from heterogeneous studies.
- The review acknowledges that the realism of dietary change scenarios is questionable.
- The cultural acceptability of eating less may prove challenging.
Conclusion
The reviewed studies emphasize the need for a holistic approach to diet sustainability, integrating nutritional adequacy, health impact, acceptability, affordability, and environmental considerations. The findings suggest that reducing meat consumption and energy intake are primary strategies for reducing diet-related greenhouse gas emissions, yet the choice of replacement foods is critical. The study underscores that high nutritional quality and low environmental impact are not always aligned, and the importance of considering the economic and social aspects of dietary changes. The research indicates that current dietary patterns, while not perfect, can be improved without radical food choices. The studies stress the scarcity of comprehensive datasets and highlight that future research should prioritize standardized data and consider various environmental impacts beyond greenhouse gases. The conclusion reinforces the potential for improving diet sustainability, especially in areas with moderate food choices such as meat reduction, by promoting food variety. The review acknowledges that the sustainability of diets is complex, with multiple dimensions that are not always compatible. The authors recommend a whole-diet approach to promote better dietary choices.