Many people choose to follow a plant-based diet for environmental reasons, so I wanted to dig into the research about how much of an impact this has.

Sustainable Eating

The food supply-chain can impact the environment in different ways, such as:

• Greenhouse gas emissions (e.g. carbon dioxide, methane and nitrous oxide) from production, transport and storage of food
• Land and water use
• Soil, air, and water quality
• Impacting on the diversity ecosystems

But the Food and Agricultural Organisation (FAO) definition if a sustainable diet is wider than just the environment, this is defined as a diet: “with low environmental impacts which contribute to food and nutrition security and to healthy life for present and future generations. Sustainable diets are protective and respectful of biodiversity and ecosystems, culturally acceptable, accessible, economically fair and affordable; nutritionally adequate, safe and healthy; while optimising natural and human resources‟¹.

Carbon Footprint

The production of meat and dairy products are the largest contributors to Green House Gas (GHG) emissions related to diet^2-5.

Beef cattle and dairy cattle release the most emissions overall^2-5. But in some countries dairy farming has made good progress in reducing GHG emissions (by 30.7% over the 25 – 30 years), due to increasing milk production per cow⁶.

Graph reference: http://www.fao.org/3/a-i3437e.pdf   

Energy input from fossil fuels used to produce 1 kcal of animal protein is more than 11 times higher than production of the same amount of grain protein⁷.

Furthermore, a study based on the UK National Diet and Nutrition Survey (NDNS) found that meat intake accounted for 31% of dietary CO2 emissions for men and 27% of  dietary CO2 emissions for women⁴.

This study also calculated that avoiding red & processed meat at a population level would reduce CO2 emissions by 27.8 million tonnes per year.

Similarly, beef and fish have been found to produce 38 times the amount of GHG emissions as compared with potatoes⁸.

Overall, it is thought that switching to a plant-based diet on a global scale would reduce greenhouse gas emissions by 49%⁹. 

Other Environmental Factors

Water-use also needs to be considered.

It takes roughly 100 times more water to produce 1 kg of animal protein as compared to 1 kg of grain protein^7.

It also takes less resources to produce most types of plant-based milks as compared with cow’s milk, but this isn’t true for all plant-based milks⁹. For example, it makes about 17 times more water to produce almond milk compared to cow’s milk per litre (although cow’s milk emits almost 10 times as much GHGs)⁹. 

Other factors related to producing plant-based foods include: use of agrochemicals (and the subsequent effect on biodiversity) and the energy used by  heat lamps^3,10.

Overall, it has been estimated that a global- shift towards plant-based diets would reduce land use by 76%.⁹

It has also been estimated that this would reduce the impact on water and by reducing acidification by 50%, and reducing eutrophication by 49%.⁹ 

Another study from 2016 found that if the UK population’s intake matched the Eatwell Guide, this would lower the overall environmental impact related to diet by 33%.¹¹

Graph reference: https://www.carbontrust.com/media/672635/phe-sustainable-diets.pdf

Fish consumption can damage the environment by disrupting ecosystems. Overfishing is a big issue, in 2012 it was announced that 87% of all fish stocks were either fully exploited or overexploited12. For more information about this, check out this post about eating fish sustainably. 

Nutritional Content

A sustainable diet also needs to be nutritionally adequate¹.

The nutritional benefits of animal-based products include:

• Good sources of protein and B-vitamins (including vitamin B12)
• Oily fish is a great source of omega-3 fat
• Red meat is a really source of bio-available iron & zinc 
• Dairy and fish are good sources of iodine
• A 200ml glass of milk provides: 31% of the daily recommended intake of calcium and 28% of phosphorus¹³  

However, a varied plant-based diet which contains a moderate amount of dairy, or calcium-fortified dairy alternatives, should provide a balanced intake of nutrients. Balanced plant-based diets are also associated with numerous health benefits. For information about how to achieve a well-balanced plant-based diet, check out my post: Nutritional Advice for Vegans & Vegetarians.

Soya milk contains a higher level of protein than other plant-based milks. A low intake of protein isn’t a concern for most people, as most already consume more protein than the recommended protein intake.  But may be an issue for those at a higher risk of malnutrition, such as older people or infants.

Image reference: PEN (2017) “Plant-based Beverages – Are They Really Healthier For Young Children?”

For more information on how to achieve a nutritionally-balanced plant based diet check out my previous posts: Nutritional Advice for Vegans and Vegetarians, and What You Need to Know About Vegetarian Meat Alternatives.

Overall:

The concept of a ‘sustainable diet’ is complex and there isn’t currently one solid set of guidelines to follow. 

Sustainable choices on an individual and group level can nudge companies to use more  environmentally-friendly methods. However, it it is worth bearing in mind that changes may need to occur higher up (e.g. at legislation and production level) to make a significant difference in terms of the environment.

But moving towards a more plant-based diet is likely to benefit the environment as well as public health.

A plant-based diet, doesn’t need to be a plant-ONLY, as sustainable eating messages don’t need to be black and white. 

A practical and realistic message to spread is for most people to eat more plants and a little less meat and dairy (i.e. follow the Eatwell Guide), rather than promoting veganism as the only environmentally-friendly option.

References:

1. FAO (2010) “Final document: International Scientific Symposium Biodiversity and Sustainable Diets: United against Hunger. 3-5 November 2010” 
2. Gerber et al. (2013) “Tackling climate change through livestock – A global assessment of emissions and mitigation. Food and Agriculture Organization of the United Nations”
3. BDA Policy Statement on Sustainable Diets (2017)
4. Aston et al. (2012) “Impact of a reduced red and processed meat dietary pattern on disease risks and greenhouse gas emissions in the UK: a modelling study“
5. Perignon et al. (2016) “Improving diet sustainability through evolution of food choices: review of epidemiological studies on the environmental impact of diets”
6. DAERA-NI (2017) “Greenhouse gas emissions Northern Ireland Dairy Farm Sector”  

7. Pimental & Pimental (2003) “Sustainability of meat-based and plant-based diets and the environment”

8. Wallen et al. (2004) “Does the Swedish consumer’s choice of food influence greenhouse gas emissions?” 
9. Poore & Nemecek (2018) “Reducing food’s environmental impacts through producers and consumers” 
10. Riley & Buttriss (2011) “A UK public health perspective: what is a healthy sustainable diet?” 
11. The Carbon Trust (2016) “The Eatwell Guide: a More Sustainable Diet”
12. FAO Fisheries and Aquaculture Department (2012) “The State of World Fisheries and Aquaculture 2012. Rome: Food and Agriculture Organization of the UN”
13. The Dairy Council (2016) “Milk Factsheet”