August 8, 2019

expert reaction to study looking at environmental impacts of plant-based and meat-based diets

Research, published in Scientific Reports, reports on the environmental impacts of diet, concluding that by replacing meat with protein-conserving plant alternatives Americans could satisfy their key nutritional requirements, while eliminating pastureland use and reducing 35-50% of the cropland currently needed for food production. 

Dr Oyinlola Oyebode, Associate Professor in Public Health, University of Warwick, said:

“This study fits with growing evidence of the multiple benefits that could accrue if people shift their diet towards plant-based alternatives to meat.  These benefits include reducing greenhouse gas emissions, and releasing land which could then be reclaimed as habitat for animal and plant species.  In addition though, there are benefits to human health.  This study looked at diets in which meat was replaced with plant foods, while exactly matching the protein consumption of the average American.  The resulting diets were different from the average American diet with respect to 16 important nutrients, but all of the differences were advantageous to health, except for the reduced vitamin B12 (which the authors suggest would need to be taken in supplement form).

“The original press release doesn’t quite match the statistics in the paper which say that if Americans swapped to the plant-based diets there would be a 35-50% reduction in three key resources (crop land use, greenhouse gas emissions and nitrogen fertilizer).  The reduction in land use would be 34%.  [This has since been amended on the Nature press site.]  There is also another error message attached to the updated press release stating that there is an error in the code that produced Figure 3, which means some of the foods are incorrectly labelled.  These two minor errors raise concerns that further errors might be uncovered, but I didn’t identify any further problems.

“It is worth noting that the authors match the average American protein consumption with their modelled diets, but actually it is highly likely that we don’t need to eat the amount of protein that an average American eats.  Also, depending on what it is possible to grow in a country, the particular diet recommended might not be optimal elsewhere.”

Dr Mark Lee, Researcher in Sustainable Livestock Production Systems, the Royal Botanic Gardens, Kew, said:

“This study is yet more evidence that it would be hugely beneficial to the environment to reduce our intake of meat.  Other studies have also shown that reducing our meat consumption, particularly red meat consumption, would also improve our health so it makes a lot of sense.  Keeping livestock and producing meat is hugely resource-intensive and contributes substantially to environmental degradation, climate change, loss of habitat for wildlife and water pollution.  Reversing this trend is one of societies key challenges.

“This study used a modelling approach to quantify the potential environmental benefits if every American replaced all of their pork, chicken and beef intake with plants.  The authors did not say this should happen; they just used a modelling approach to estimate what the benefits might be if it did.  A unique aspect of this study is that the authors included many different nutritional components in their models, rather than just protein, to show that plants could replace meat in our diets and still deliver most of nutrition that we need.  They provide compelling evidence that a shift to plant-based diets could have a huge benefit to the environment because less fertiliser and land would be needed, and our greenhouse gas emissions would be reduced – reducing the environmental footprint of our agricultural systems.

“For example, they calculated that if every American replaced beef with plant alternatives then this could save approximately 29 million hectares of cropland, 3 billion kilograms of nitrogen (for example in fertilisers) and 280 billion kilograms of the potent greenhouse gas, carbon dioxide (and its equivalents).  I do not think that we should totally eliminate meat from our diets.  Meat is important to many of us, and meat has been a part of our culture and tradition for thousands of years.  We also get some essential dietary components from meat, such as fatty acids, selenium, zinc and vitamin B12.  But, there is now overwhelming evidence that reducing our meat intake and carefully selecting plants to replace that meat based on their nutritional profile would have a huge benefit to our environment and to our health.  If we reduced our meat consumption we could move to more sustainable, low intensity, wildlife friendly livestock farming systems, which would further drive down the environmental footprint of our diets.  Now is the time for governments to act and promote the benefits of reducing our meat consumption and to invest in high-quality, sustainable livestock farming.”

Prof Alan Dangour, Professor in Food and Nutrition for Global Health, London School of Hygiene & Tropical Medicine, said:

“Today’s IPCC report on Climate Change and Land identifies the enormous impact that our dietary choices have on the environment – it is clear that reducing the demand for meat in diets is an important approach to lowering the environmental impact of the food system.

“This new analysis identifies the environmental impact of swapping meat for vegetable sources of protein in the US diet.  Unfortunately, the published paper contains multiple errors (for example, the identification of pears, green peppers and strawberries as major sources of vegetable protein) that make it very hard to interpret and the findings at this stage should be treated with caution.”

Prof Michael Lee, livestock scientist, and Head of Sustainable Agricultural Sciences at North Wyke, Rothamsted Research, said:

“This paper oversimplifies the complex issue of the role of livestock in sustainable food production by advocating complete removal, but this issue is far from black and white.  The research doesn’t fully considering the unintended consequences of such dietary transitions especially in relation to land use change with subsequent impacts on soil health and the releasing of carbon stocks built up within pasture soils, which are one of the healthiest on the planet due to their high organic matter content.

“The authors’ approach is predicated on the assumption that all livestock (ruminant predominately) production is unsustainable and equally plant-based alternatives are in comparison environmentally benign.  However, this is not true as shown by the two main plant sources required to replace livestock protein and fat – namely soya and palm oil – both of which have been responsible for some of the greatest biodiversity loss on the planet through deforestation needed for their cultivation.

“Ultimately the paper professes that complete replacement of livestock products with plant alternatives is possible and would in fact increase the ‘plant-rich’ nutrients in the diet of meat eaters.  However, they conclude that such a diet would be limiting in many ‘animal-rich nutrients’ such as long chain fatty acids, zinc, selenium and Vitamin B-12.  Therefore, the obvious conclusion is for a balanced diet which contains predominately plants with a responsible level of favourably sourced animal products which do not compete for human edible sources, such as pasture-based beef and lamb.

“Not all livestock are produced in the same way and we need to differentiate when providing consumers with information.”

Dr Taro Takahashi, researcher at Rothamsted Research, and Senior Lecturer in Sustainable Livestock Systems and Food Security at the School of Veterinary Sciences, University of Bristol, said:

“While I agree with the study’s ultimate message that we currently consume too much meat, I question the logic employed by the authors to scientifically reach this conclusion.  They compare environmental impacts of the current US diet against the mathematically minimal level of pollution arising from hypothetical plant-based diets that satisfy certain nutritional conditions.  This is not an apple-to-apple comparison.

“What they should have done, in my view, is to allow meat to also be part of the choice set from which the environmentally optimal diets are formulated, and then investigate how much meat we should eat, or perhaps should not eat, to minimise environmental impacts while appropriately feeding ourselves at the same time.

“I also challenge the accuracy of information the authors chose to communicate to the general public through this press release.  As part of the mathematical process to select environmentally optimal plant-based diets, they arbitrarily relaxed human requirements for selenium, choline, monounsaturated fatty acids, niacin and cobalamin, of which contents are known to be generally smaller in plant-based products than animal-based products.  While I understand the mathematical need for this change to make research operational, this is a serious limitation of the study that should have been communicated far more clearly and prominently.”

‘Environmentally Optimal, Nutritionally Sound, Protein and Energy Conserving Plant Based Alternatives to U.S. Meat’ by Gidon Eshel et al. was published in Scientific Reports at 14:00 UK time on Thursday 8 August 2019. 

DOI: 10.1038/s41598-019-46590-1

Declared interests

Dr Oyinlola Oyebode: “I don’t have any declarations of interest.”

Dr Mark Lee: “No declarations of interest.”

Prof Alan Dangour: “I am the Director of the LSHTM Centre on Climate Change and Planetary Health.  I receive competitive grant funding to conduct research on the links between the environment, food systems and health.”

Dr Taro Takahashi: “I declare no conflict of interest associated with this research or my comment.”

Prof Michael Lee and Dr Taro Takahashi: Rothamsted undertakes some livestock industry research collaborations, mainly through the Centre for Innovation Excellence in Livestock (CIEL).