Plant-based diets; the optimal choice for planetary health

The Intergovernmental Panel on Climate Change (IPCC) warns us about the dire consequences of the projected global warming of 1.5 °C above pre-industrial levels, which could happen in less than 12 years time. This includes extreme heat, increased and more frequent flooding and droughts, rising sea levels, species loss and extinction and risks to human health, livelihoods, food security, water supply, human security, and economic growth. Our diet choices directly impact environmental and planetary health.

The current global food and agriculture system is a major driver of climate change, water pollution, land degradation, loss of wildlife and biodiversity, deforestation and ocean destruction. Animal agriculture produces more greenhouse gas emissions than all forms of transportation combined. One of the most comprehensive analyses of the global farming system, assessing all aspects of the food chain from ‘farm to fork’, concluded that shifting to a plant-based diet would have the most impact on planetary health than any other driver of climate change. Meat and dairy production uses 83% of farmland and produces 60% of agricultural greenhouse gas emissions, whilst only providing 18% of calories and 37% of protein. Even the production of meat and dairy with the lowest environmental footprint is less sustainable that the worst performing plant food source. Fresh water fishing and grass fed beef, generally considered more sustainable, was found to have a greater environmental effect than once thought and creates more greenhouse gas emissions than any plant food source. Further studies have examined the impact of shifting towards plant-based diets on both human and environment health and concluded definitively that it would provide combined benefits. Plant-based diets could reduce green house gas emissions by 56% and other environmental impacts of the food system by 6–22%, whilst at the same time improving the nutritional quality of our diet and significantly reducing the burden of chronic disease and reducing premature mortality by 22%.

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Most recently, the Eat-Lancet Commission has developed global scientific targets that brings together recommendations for a global healthy reference diet, produced from sustainable food systems, to ensure that the United Nations Sustainable Development Goals (United Nations, 2016) and Paris Agreement (United Nations Convention on Climate Change, 2015) are achieved. The reference diet, termed the planetary health plate, consists mainly of whole plant foods, with low amounts of animal-derived and processed foods. Meat and dairy is considered optional and if consumed should provide <15% of total calories. It estimates that the global adoption of this reference diet would prevent around 11 million deaths a year or 23% of adult deaths, whilst keeping the global food system within planetary boundries.

Planetary health plate

Another major issue with our current food system, which threatens global health, is the widespread use of antibiotics in animal agriculture. Around 40–70% of all antibiotics globally are sold for use in animals and it has been recognised for many years that agricultural use of antibiotics is a major contributor to antibiotic-resistant infections in humans. We are entering a post-antibiotic era where it is no longer unusual to be treating patients with infections for which there are no suitable antibiotics. A review of antibiotic resistance commissioned by the UK Prime Minister, reported in 2016. It suggested that globally, 700,000 lives are lost annually from antibiotic-resistant infections and by 2050 the number could be as high as 10 million. One of its 10 recommendations is the reduction of antibiotic use in animal agriculture. However, with the increasing industrialisation of food production and the growing demand for meat, this will be impossible to achieve without Governments working together. This is a global issue, which requires a global solution, and reducing antibiotic resistant organisms in our food system needs to be a priority.

Despite the widespread use of antibiotics in animal agriculture, food-borne infections (bacteria, viruses, protozoal) continue to be a major cause of morbidity and mortality worldwide, with most due to contamination of animal-derived foods or plant-foods that have been contaminated by the manure of food animals. One of the most comprehensive studies of the worldwide burden of food-borne illnesses estimated that in 2010 there were 582 million cases of infection caused by contaminated food, with 351,000 deaths. In 2018, there were nearly 50,000 cases of foodborne infection in the European Union with 1 in 3 cases caused by Salmonella, mainly linked to the consumption of eggs.

Industrialisation of animal farming along with habitat destruction has led to the perfect conditions necessary for the transmission of novel infections, mostly viruses, from animals to humans with epidemic and pandemic potential. At the time of writing, COVID-19 has caused a global and catastrophic pandemic, yet this is just one of several zoonotic pandemics that have occurred in the last century that can be traced back to our farming practices and the use of animals as food (see image below).

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Of course a sustainable diet is much more than one that is optimal for health and the environment. Other socioeconomic factors are just as important. The Food and Agricultural Organization (FAO) has a definition that includes aspects of food and nutrition security, culturally acceptability, accessibility, economic fairness and affordability. Current levels of food waste are also unsustainable. For example, the EU food waste is 89 million tonnes a year, worth about £950 per household. Globally, approximately a third of food is wasted across the supply chain with 70% of this waste occurring in the home.

Key components of a sustainable diet, FAO

It is encouraging to see that Government and national and international organisations are increasingly considering aspects of sustainability when making dietary recommendations. The Public Health England 2016 dietary guidelines, called the Eatwell guide, considered the environmental sustainability of its recommendations and was able to show that adherence to the Eatwell dietary guide would have a lower environmental impact than the typical UK diet. The BDA (the association of UK dietitians) has launched its One Blue Dot campaign, a project aimed at promoting environmentally sustainable diets and providing toolkits for its members to use when advising patients and clients. Most recently, the Health Canada dietary guidelines not only emphasise and recommend an environmentally sustainable diet centred around whole plant-foods but also emphasises the importance of practical food skills and the importance of creating supportive environments for healthy eating, such that nutritious food is affordable and accessible to all. Note that dairy has been removed from the plate and plant sources of protein are emphasised over animal sources.

Health Canada food guide

Of course, when you consider the environmental sustainability of vegetarian and vegan diets there is a significant advantage. Analysis from the Adventist Health Study-2 (AHS-2) and the EPIC-Oxford study shows that greenhouse gas emissions are 29% lower for vegetarian diets in the AHS-2 and 47–60% lower for vegetarian/vegan diets in EPIC-Oxford compared to non-vegetarian diets (image below).

Recommendations for fish consumption are where health and environmental considerations diverge. Most dietary guidelines continues to recommend the consumption of fish once or twice a week, including the recently published Eat-Lancet commission reference diet. The regular consumption of fish does have positive health impacts, predominantly because it is replacing other less healthy foods, such as red and processed meat in the diet, and is a source of unsaturated fats, including long chain omega-3 fatty acids. Whether the addition of fish to a predominantly plant-based diet improves health outcomes above and beyond the benefits of eating whole plant foods is not known. However, it is not thought to be necessary and nutritional requirements can be met without consuming fish. Essential long chain omega-3 fatty acids are the mostly commonly cited reason for continuing to consume fish. However, they can be obtained straight from the source, marine algae, or from the precursor short chain omega-3 fatty acid, alpha-linolenic acid, found in plant-foods, including walnuts, chia and flax seeds. For a global population of over 7 billion to eat fish 1–2 times a week is unlikely to be sustainable given that 90% of world fish stocks are fully or over-exploited from fishing. In addition, there are concerns over mercury and other fat-soluble pollutant (polychlorinated biphenyls and dioxins) contamination of fish and shellfish, particularly larger fish that are higher up the food chain. Mercury in particular is associated with neurological toxicity.

The international community has called Health Professionals to action. The Eat-Lancet commission urges health professional to consider both health and environmental sustainability when counselling patients about diet and recommends advising the shift to more plant-based diets. The World Organization of Family Doctors (WONCA) have published a “Declaration Calling for Family Doctors of the World to Act on Planetary Health”. This involves advising patients to transition to a more plant-based diet in line with the Eat-Lancet planetary health diet.

It is not only important to shift to a plant-based diet but also to increase the variety of foods in the diet. The WWF, a leading independent conservation organisation, have produced a report highlighting the need to diversify our diet. You can find their report here, which highlights 50 foods we should eat more of because they are nutritious and have a lower impact on the environment, whilst increasing the diversity of our diet and farming systems. Not all of these foods are currently easily accessible but by making a conscious choice to consume more of these foods we may be able to help safeguard these foods for future generations.

For the health of our planet and for human and non-human animals that share this world, a global transition to a plant-based dietary pattern has become an imperative.

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