Abstract
To maintain planetary health, human activities must limit the use of Earth’s resources within finite boundaries and avoid environmental degradation. At present, food systems account for a substantial use of natural resources and contribute considerably to climate change, degradation of land, water use, and other impacts, which in turn threaten human health through food insecurity. Additionally, current dietary patterns, rich in animal products and excessive in calories, are detrimental to both population and planetary health. In order to resolve the diet-environment-health trilemma, population-level dietary changes are essential. Vegetarian diets are reported to be healthy options. Most plant-sourced foods are less resource intense and taxing on the environment than the production of animal-derived foods, particularly meat and dairy from ruminants. This review article explores simultaneously the environmental sustainability of vegetarian diets, and its alignment with people’s health. In general, the progression from omnivorous to ovolactovegetarian and vegan diets is associated with increased environmental sustainability. Greenhouse gas emissions resulting from vegan and ovolactovegetarian diets are ~50% and ~35% lower, respectively, than most current omnivore diets, and with corresponding reductions in the use of natural resources. Concomitant health benefits could be obtained by shifting from current dietary patterns to sustainable vegetarian diets. Thus, there seems to be an alignment of health and environmental outcomes for vegetarian diets. Although this shows the human health and environmental sustainability benefits of vegetarian diets in high-income countries, questions remain about the challenges in other contexts and the political will to promote meat-free diets as the social norm. Adv Nutr 2019;10:S380-S388.
Generated Summary
This review article, published in Advances in Nutrition, explores the environmental sustainability of vegetarian diets and their alignment with human health. The study is a review of the existing literature, focusing on studies published from 2000 to October 2018, identified through keyword searching strategies using PubMed and relevant journals and books. The research aims to assess the environmental impact of vegetarian diets, specifically focusing on greenhouse gas (GHG) emissions, land use, and water use, and how these factors relate to human health. The study includes both ovolactovegetarian (excluding meat and fish but including eggs and dairy) and vegan (excluding all animal products) diets. The review also considers the projected dietary patterns of a country based on actual consumption tendencies, comparing them with vegetarian dietary scenarios to evaluate environmental impacts.
Key Findings & Statistics
- The food system significantly contributes to climate change and environmental degradation. It accounts for a substantial use of natural resources.
- Current global dietary patterns, rich in animal products and calories, are detrimental to both population and planetary health.
- Vegetarian diets are reported to be healthy options.
- Compared to current omnivore diets, vegan and ovolactovegetarian diets have ~50% and ~35% lower greenhouse gas emissions, respectively, and a corresponding reduction in the use of natural resources.
- The study found 25 studies focused on GHG emissions, 13 on land use, and 11 on water use.
- The median reductions in GHG emissions by shifting from the current diet to ovolactovegetarian and vegan diets were -35% (range: -13%, -85%) and -49% (range: -23%, -89%), respectively.
- Shifting to ovolactovegetarian and vegan diets would achieve a reduction in land use of -42% (range: -27%, -74%) and -49.5% (range: -29%, -80%), respectively.
- The median reduction in water use by shifting to an ovolactovegetarian diet was -28% (range: -7%, -52%).
- One study showed an increment of +85% regarding water use.
- Reducing GHG emissions by the food system is important, as it accounts for 20-30% of total anthropogenic GHG emissions.
- The food system accounts for 70% of all freshwater use and is a major source of water pollution.
- About 80% of the world’s deforestation is related to the food system.
- Without corrective measures, the environmental impact of the food system could increase by 50–90% in 30 years.
- Vegetarians have a lower incidence of type 2 diabetes, obesity, coronary heart diseases, and other noncommunicable diseases, and greater life expectancy.
- The production of 1 kg of beans requires 3.8 m² of land, 2.5 m³ of water, 39 g of fertilizer, and 2.2 g of pesticide, while beef requires 52 m² of land, 20.2 m³ of water, 360 g of fertilizer, and 17.2 g of pesticide.
- Comparing 1 kg of protein from beef and beans, beef protein requires 18, 10, 12, and 10 times more land, water, fertilizers, and pesticides.
- The GHG emissions reductions estimated for these dietary patterns were ~10%, considerably less than those obtained by changing to vegetarian diets.
Other Important Findings
- The study highlights that vegetarian diets, particularly vegan diets, have increased environmental sustainability and are associated with health benefits.
- The study uses the term “diet-environment-health trilemma” to draw attention to the challenges created by the apparently unrelated entities of diet, environment, and health.
- A growing body of literature explores improvements in agricultural technology, reductions in food losses and waste, and shifting food choices and diet patterns of individuals and populations to address these challenges.
- Changes in individual eating habits are deemed necessary to address the environmental impacts of the food system.
- The study defines a “sustainable diet” as a pattern with low environmental impact that contributes to food and nutrition security and to healthy life.
- The Academy of Nutrition and Dietetics recognizes that a well-planned vegetarian diet is healthful and nutritionally adequate, being appropriate for human growth and development.
- Meat-free diets are suitable not only in the prevention but also in the treatment of many diseases.
- Animal-derived foods, particularly meat and dairy from ruminants, are resource-intensive and more taxing on the environment compared with the production of most plant-based foods.
- The study acknowledges the need to assess the sustainability of vegetarian diets according to the specific foods actually consumed by individuals, not by the average nominal diets.
- The study suggests that shifting from current dietary patterns to vegetarian diets, especially vegan, would be an effective measure to halve GHG emissions, as suggested by IPCC.
- The environmental benefits would ultimately depend on the specific foods included in a diet.
Limitations Noted in the Document
- The study acknowledges that the environmental benefits depend on the specific foods consumed in a vegetarian diet.
- The study notes that there is a limited number of studies reporting on both environmental and health outcomes of vegetarian diets simultaneously, which limits the strength of conclusions.
- The study primarily focuses on GHG emissions and acknowledges the need to assess other environmental factors, such as ozone layer depletion or biodiversity loss, for a more complete understanding of the sustainability of dietary patterns.
- The study highlights that most research on diet sustainability has been conducted in high-income countries, and the data may not be directly applicable to low- and middle-income countries.
- The study notes the challenge of drastically reducing meat consumption in societies where daily meat consumption is the social norm.
- The study’s conclusions are based on the existing literature, which may not fully capture all relevant research.
- The study acknowledges the difficulty in changing food habits.
Conclusion
The study’s findings support the idea that adopting vegetarian diets can offer both environmental sustainability and health benefits. Specifically, the progression from omnivorous to ovolactovegetarian and vegan diets is associated with increasing environmental sustainability, with the latter showing the most significant reductions in GHG emissions, land use, and water use. These dietary changes also align with improved health outcomes. However, it emphasizes that the sustainability and health benefits depend on the specific composition of the diet, as the impacts of individual foods vary greatly. The review stresses the importance of reducing animal-sourced foods, particularly red meat, to achieve the goal of zero net emissions by 2050, as suggested by the Intergovernmental Panel on Climate Change (IPCC). The study highlights a significant correspondence in the direction of reported findings: fewer animal products correlate with more sustainable diets. Nevertheless, the study acknowledges the need for further investigation into the environmental and health outcomes of vegetarian diets, particularly with a focus on the specific foods within these diets. It underscores the complexity of the issue and the importance of considering cultural and socioeconomic factors when promoting dietary changes. The review suggests that population-level vegetarian patterns have the potential to address the diet-environment-health trilemma, thereby contributing to a more sustainable food system and improved public health. The authors emphasize that the aggregate dietary decisions a society makes have a large influence on climate change and other environmental impacts. The research stresses the need to better understand the cultural and socioeconomic factors that influence changes in dietary patterns. It also suggests the need for further research to optimize meat-free diets, achieving the maximum health and environmental benefits. The study concludes that the current dietary patterns should be shifted to vegetarian diets, to improve both people and planetary health.