On food diets, carbon footprints and health: a complex issue

By Clemence Blanchard

Whether or not we are aware – or care – about it, food contributes substantially to greenhouse gas (GHG) emissions. In spite of this, food remains at the center of our lives, health and culture-wise – and will continue to do so in the future. This issue is currently exacerbated by our growing world population and food security problems. On the flipside, we are seeing a decline in meat and dairy consumption in the UK, with vegetarian and vegan diets on the rise (Benson et al., 2019). Vegetarians remove all meat products from their diets, with vegans additionally removing any animal-based products like dairy and eggs. While many shift to these plant-focused diets for animal welfare reasons, others see a real advantage to our planet: reducing our dietary carbon footprints. This shift poses some interesting questions on our food diets, their environmental impacts, and their nutritional values that deserve to be addressed. 

GHG emissions are released throughout the entire chain of food production and consumption, from transport to storage and even wastage. Carbon dioxide is released from transportation vehicles and production machinery; methane is released from livestock and fermentation processes; nitrous oxide is released from soil tillage (soil-turning), the list continues (Scarborough et al., 2014). In 2008, the Food Climate Research Network (FCRN) reported that food consumption in the UK accounts for 19% of GHG emissions in the goods and services category, though this is heavily emphasised to be an estimate only (Garnett, 2008). This has important implications, especially when considering whether all food products have an equal weighting in this ‘overall’ carbon footprint. 

It is generally acknowledged that animal-based products release greater emissions per unit weight when compared to plant-based products. This is in part based on the conversion efficiency of plant into animal matter standing at roughly 10%, where livestock is often fed on grain or plant protein (Godfray et al., 2010). This logic envisages that a larger number of people could be fed using the same amount of land if they converted to a vegetarian diet. Hypothetically, this would not only alleviate food security issues, it would also lower the environmental impact of our food. In reality, it is not quite as simple: livestock is also grass-fed and land conversion from grassland to arable land is not inconsequential. Nevertheless, the consensus remains that GHG emissions are higher for meat production. Poore & Nemecek (2018) in their study on reducing the carbon footprint of food through both producers and consumers make a few points. Feed emissions tend to be higher than those for vegetable protein farming; soy and maize agriculture for feed production play a large role in deforestation; and enteric fermentation as part of digestion for ruminating animals releases additional GHG emissions. Additionally, a cohort study on the gas emission impact of various diets found that a high-meat diet releases 2.5 times the GHG emissions of a vegan diet. This was adjusted for sex, age and standardised to a 2,000 kcal diet (Scarborough et al., 2014). It was also suggested that a shift from a high to low-meat diet could reduce the carbon footprint by 920 kgCO2e every year where CO2e stands for carbon dioxide equivalent – a unit for the global warming potential (GWP) of greenhouse gases in terms of the GWP of CO2 which is 1. If anything, this should incentivise many to consider the impact that the meat they eat has on the environment. 

In terms of nutritional and health value, it is generally accepted that if appropriately implemented and planned for nutrients, both vegetarian and vegan diets are nutritionally adequate and considered healthy (even for children). This is corroborated by the NHS in their Eatwell guide (NHS, 2018). A plethora of European Prospective Investigation Into Cancer & Nutrition (EPIC)-Oxford studies suggest that there may be advantages to such diets: there are associations between the vegetarian diet and lower risk of ischemic heart disease hypothesised to do with ‘good’ HDL cholesterol and systolic pressure (Crowe et al., 2013), and lower risk of specific cancers for both vegetarians and fish eaters compared to meat eaters (Key et al., 2014), though some associations found are not significant. 

On the contrary, a study by Tong et al. (2020) found that fractures, which become a common issue in adulthood, are higher in vegans, vegetarians and fish eaters. Vegans especially were found to have total higher risk of fractures, but specifically, leg, hip and vertebra fractures. This is somewhat attributed to lower bone density and lower calcium levels, despite the study having accounted for BMI and overall lower protein and calcium levels, which begs the question of what other factors could be unaccounted for. What this comes down to is the fact that although vegetarian and vegan diets can be adequate if properly implemented it is hard to gauge whether this is actually the case for most people. Certainly, one’s protein requirements can be fulfilled with more ease on a diet including meat. 

We can see just how complex this issue is when comparing the carbon footprints of dietary guidelines around the world which, despite our shared biology, differ. The US may have a much higher carbon footprint of 3.83 kgCO2e/d compared to India’s 0.86 kgCO2e/d but recommends twice as many protein foods, and six times the amount of dairy compared to Oman with 2.53 kgCO2e/d (Kovacs at al., 2021). It seems unfair to take the US diet result at face-value when the resulting protein/nutrient content may be higher, but the question still remains whether the US diet is ‘better’ to begin with.

Overall, the evidence points towards an environmental and health advantage to eating less animal-derived products, and there is little sacrifice involved in making small changes toward this, however, it is important to consider all aspects and remain aware that this situation is not quite as simple as it may seem. Nuts for example release high proportions of GHG emissions and can be low-yielding (cashews) and water, fertiliser, and pesticide intensive (almonds) (Poore & Nemecek, 2018).  


Benson, A., Irdam, D., Bulceag, I., Barber, T. & Draper, A. (2019) The Food and You Survey: Wave 5, Secondary Analysis: The Current Food Landscape across England, Wales and Northern Ireland. Food Standards Agency. Available from: https://food.gov.uk/sites/default/files/media/document/food-and-you-wave-5-secondary-analysis-current-food-landscape.pdf [Accessed 22/06/2021]

Scarborough, P., Appleby, P.N., Mizdrak, A., Briggs, A.D.M., Travis, R.C., Bradbury, K.E. & Key, T.J. (2014) Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK. Climatic Change. 125 (2), 179-192. Available from: 10.1007/s10584-014-1169-1

Garnett, T. (2008) Cooking up a storm: Food, greenhouse gas emissions and our changing climate. Food Climate Research Network Centre for Environmental Strategy. Available from: https://tabledebates.org/sites/default/files/2020-10/CuaS_web.pdf [Accessed 22/06/2021]

Godfray, H.C.J., Beddington, J.R., Crute, I.R., Haddad, L., Lawrence, D., Muir, J.F., Pretty, J., Robinson, S., Thomas, S.M. & Toulmin, C. (2010) Food Security: The Challenge of Feeding 9 Billion People. Science. 327 (5967), 812-818. Available from: 10.1126/science.1185383

Poore, J. & Nemecek, T. (2018) Reducing food’s environmental impacts through producers and consumers. Science. 360 (6392), 987-992. Available from: 10.1126/science.aaq0216

NHS. (2018) Vegetarian and vegan diets Q&A. Available from: https://www.nhs.uk/live-well/eat-well/vegetarian-and-vegan-diets-q-and-a/ [Accessed 22/06/2021]

Crowe, F.L., Appleby, P.N., Travis, R.C. & Key, T.J. (2013) Risk of hospitalization or death from ischemic heart disease among British vegetarians and nonvegetarians: results from the EPIC-Oxford cohort study. American Journal of Clinical Nutrition. 97 (3), 597-603. Available from: 10.3945/ajcn.112.044073

Key, T.J., Appleby, P.N., Crowe, F.L., Bradbury, K.E., Schmidt, J.A., Travis, R.C. (2014) Cancer in British vegetarians: updated analyses of 4998 incident cancers in a cohort of 32,491 meat eaters, 8612 fish eaters, 18,298 vegetarians, and 2246 vegans. American Journal of Clinical Nutrition. 1 (1), 378S-385S. Available from: 10.3945/ajcn.113.071266

Tong, T.Y.N., Appleby, P.N., Armstrong, M.E.G., Fensom, G.K., Knuppel, A., Papier, K., Perez-Cornago, A., Travis, R.C. & Key, T.J. (2020) Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study. BMC Medicine. 18, 353. Available from: 10.1186/s12916-020-01815-3

Kovacs, B., Miller, L., Heller, M.C. & Rose, D. (2021) The carbon footprint of dietary guidelines around the world: a seven country modelling study. Nutrition Journal. 20, 15. Available from: 10.1186/s12937-021-00669-6

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