Abstract
Abstract: The food that we consume has a large impact on our environment. The impact varies significantly between different diets. The aim of this systematic review is to address the question: Which diet has the least environmental impact on our planet? A comparison of a vegan, vegetarian and omnivorous diets. This systematic review is based on 16 studies and 18 reviews. The included studies were selected by focusing directly on environmental impacts of human diets. Four electronic bibliographic databases, PubMed, Medline, Scopus and Web of Science were used to conduct a systematic literature search based on fixed inclusion and exclusion criteria. The durations of the studies ranged from 7 days to 27 years. Most were carried out in the US or Europe. Results from our review suggest that the vegan diet is the optimal diet for the environment because, out of all the compared diets, its production results in the lowest level of GHG emissions. Additionally, the reviewed studies indicate the possibility of achieving the same environmental impact as that of the vegan diet, without excluding the meat and dairy food groups, but rather, by reducing them substantially.
Generated Summary
This systematic review aimed to address the question: Which diet has the least environmental impact on our planet? The review compared vegan, vegetarian, and omnivorous diets, analyzing 16 studies and 18 reviews. The methodology involved searching electronic bibliographic databases (PubMed, Medline, Scopus, and Web of Science), applying fixed inclusion and exclusion criteria, and conducting a narrative synthesis of the findings. The studies ranged from 7 days to 27 years and were primarily conducted in the US and Europe. The environmental impact of the diets was assessed using three main indicators: Greenhouse Gas Emissions (GHGEs), land use, and water footprint. The focus was on understanding how these diets affect the environment, particularly concerning the production and consumption of food. Both the LOV and vegan diets were referred to as plant-based diets. The results underscore the environmental impact of different diets, with the vegan diet demonstrating the lowest CO2eq production per 2000 kcal consumed. The study highlights the need to transition towards a more sustainable food system and consumption practices.
Key Findings & Statistics
- Red meat production generates approximately 23% of agriculture-related GHGEs.
- In the US, about 31% of CH4 emissions are generated from enteric fermentation (primarily cows) and manure management.
- On average, 43 kg of GHGEs released during the production of each kg of beef. Of these 43 kg, approximately 22 kg are methane emissions.
- Meat production generates far more GHGEs than production for vegan and LOV diets.
- Beef production requires 42 times more land use, 2 times more water use and 4 times more nitrogen, while it generates 3 times more GHGEs than the staple plant foods.
- Meat and dairy production processes account for 80% of all GHGEs from the food sector and 24% of total GHGEs.
- Meat and cheese production contribute around 40% to daily GHGEs.
- High meat consumers were responsible for 1.9 times and average meat consumers were responsible for 1.5 times more GHGEs than people on LOV diets, and 2.5 and 2 times more GHGEs, respectively, than vegan consumers.
- If the beef, dairy, pork, poultry and eggs consumed in an average European diet were reduced by 50% of and replaced with a 50% higher bread intake, the amount of GHGEs emitted could be reduced by over one-third.
- Meat production accounts for 39% of land use related to human diet.
- Meat production accounts for 39% of land use related to human diet. Moreover, compared to a LOV diet, the inputs needed to produce a non-vegetarian diet are: 2.9 times more water, 2.5 times more primary energy, 13 times more fertilizer and 1.4 times more pesticides.
- Livestock farming uses 70% of agricultural land overall and a third of arable land.
- Animal protein production requires 4.4 times as much water.
- Producing each kg of consumable beef requires about 13 kg of grain and 30 kg of hay, which in turn require 105,400 L of water.
- In terms of fossil energy used in the whole process, the input needed to produce 1 kcal of plant protein is 2.2 kcal.
- One analysis shows that high meat eaters in the UK had 1.9 times and medium meat eaters had about 1.5 times more of GHGEs than an LOV, and that the food consumed by high meat eaters is associated with 2.5 times more GHGEs that that consumed by a vegan, and even average meat eaters are responsible for twice as many GHGEs.
- A second study reports similar conclusions, based on the number and composition of 2000 kcal consumed in various diets: 7.19 kg for high meat eaters (100 g of meat per day or more), 5.63 kg for medium meat-eaters (50–99 g of meat per day), 4.67 kg for low meat-eaters (less than 50 g per day), 3.81 kg for vegetarians, and 2.89 kg for vegans.
Other Important Findings
- The vegan diet is the optimal diet for the environment because, out of all the compared diets, its production results in the lowest level of GHG emissions.
- The reviewed studies indicate the possibility of achieving the same environmental impact as that of the vegan diet, without excluding the meat and dairy food groups, but rather, by reducing them substantially.
- The environmental impact of OMN production can be measured in several ways, of which we focus on three: GHGEs, land use and water footprint.
- Production for vegan and LOV diets contributes fewer GHGEs.
- Differences in the type of meat consumed can also be seen with multiple studies supporting an increase in GHGEs in diets with high amounts of ruminant meat consumption.
- A reduced consumption of animal-based products, and an increased vegetable intake show lower GHGEs.
- Diets with low meat and low processed food consumption have lower GHGEs than their counterparts.
- Beef production requires a vastly larger amount of resources than the staple plant foods such as rice, beans, and potatoes.
- The land used to produce protein from plants is much lower than the production of proteins from animals.
- Meat, as well as eggs, generates water shortage.
- Vegan diets are often associated with lower GHGEs as they do not consume any animal products.
- A plant-based diet that requires products from all over the world will have a footprint equivalent to a moderate meat eater.
- The origin and mode of transport of fruits and vegetables has a big impact on their contribution to GHGEs, which can vary a lot.
- Vegan diets produce 33% and 53% lower emissions for the same number of calories (2000 kcal) as the average US diet.
- Consuming legumes for protein instead of meat has a beneficial environmental impact, and it is also a lot cheaper.
- If beans were substituted for beef, then 692,918 km2 of US cropland could be freed up for other uses and GHGEs from this land would decrease by 74%.
- If a replacement of all meat and dairy products by plant-based food would take place, land use could be reduced by 50%.
- Most studies demonstrate that, in general, vegan diets are the most environmentally sensitive.
Limitations Noted in the Document
- The method used allowed for only one search, with the same keywords in each database. As a result, certain articles that are relevant to the subject of the paper may have been overlooked.
- The choice of search words could also have placed undesired limits on the results generated.
- Some high-quality studies are inevitably missing from this paper.
- This review is limited to assessing the relationship between three diets and only three among the many environmental factors that are affected by dietary choices.
- Most of the papers are from high-income countries, and several others including global data, and are therefore unable to assess the environmental consequences of food production in low-income countries.
Conclusion
The systematic review of vegan, vegetarian, and omnivorous diets reveals a clear difference in their environmental impacts, particularly concerning GHGEs. The findings consistently indicate that the vegan diet has the lowest environmental footprint, primarily due to the absence of animal product consumption. The production of animal-based foods contributes significantly to GHGEs, land use, and water consumption, making plant-based diets more sustainable. The research underscores the importance of reducing meat and dairy consumption to mitigate environmental impacts, with plant-based diets offering a pathway to sustainability. However, the review also acknowledges that the environmental benefits of a vegan diet can be diminished if it relies heavily on processed, plant-based substitutes, highlighting the significance of consuming unprocessed, nutritious foods. The study emphasizes that, in general, a vegan diet has the least environmental impact, but, for this to be effective, local products that minimize the environmental impact of transport should be preferred. Further research should focus on the GHGEs from different types of plant-based foods, and modified omnivorous diets with the same environmental impact as the impact from vegan diet.
IFFS Team Summary
- A comparison of vegan, vegetarian and omnivorous diets. This systematic review is based on 16 studies and 18 reviews
- Most studies carried out in US or Europe
- “In conclusion, a 100% plant-based diet (e.g. vegan) has the least environmental impact. Therefore, this [systematic] review further supports the wealth of existing evidence supporting a transition to a more sustainable food system and food consumption”