Some Science Behind Plant-Based Diets

Global dietary patterns are increasingly transitioning from predominantly plant-based, fresh foods towards higher shares in sugar, fat, and animal products, often featuring processed foods (Bodirsky et al., 2020). Especially in "western diets", chronic diseases linked to over-consumption, such as diabetes and heart disease, are an increasing public health risk (GBD, 2016), while undernourishment remains a concern due to population growth (FAO et al., 2018). Currently, poor diets are the top global health risk, and adopting healthier eating habits could prevent 11–12 million premature deaths each year (Willett et al., 2019).

At the same time, the global food system is a major driver of both climate change and environmental degradation. Food systems are responsible for a third of global anthropogenic GHG emissions (Crippa et al., 2021), and food production drives land-use changes, and biodiversity loss, the depletion of freshwater resources, and the pollution of both aquatic and terrestrial ecosystems due to fertilizer and manure use (Springmann et al., 2018).

Within food systems, the livestock sector is the dominating factor for GHG emissions and environmental degradation. The production of animal-based food accounts for 57% of emissions from the global food system (Xu et al. 2021), driven in particular by methane emissions from enteric fermentation by ruminants (Stehfest et al. 2009). Additionally, livestock production drives deforestation for grazing and feed crops, impacting biodiversity, and leads to soil degradation, water pollution, and excessive freshwater use (Steinfeld et al., 2006).

References:
^{• Bodirsky, Benjamin Leon, Jan Philipp Dietrich, Eleonora Martinelli, Antonia Stenstad, Prajal Pradhan, Sabine Gabrysch, Abhijeet Mishra, et al. 2020. ‘The Ongoing Nutrition Transition Thwarts Long-Term Targets for Food Security, Public Health and Environmental Protection’. Scientific Reports 10 (19778 (2020)). https://doi.org/10.1038/s41598-020-75213-3.
• GBD 2015 Risk Factors Collaborators. Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990–2015: A systematic analysis for the global burden of disease study 2015. Lancet 388, 1659–1724 (2016). https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(16)31679-8/fulltext.
• Willett, W. et al. Food in the Anthropocene: The EAT–Lancet Commission on healthy diets from sustainable food systems. Lancet https://doi.org/10.1016/S0140-6736(18)31788-4 (2019).
• Crippa, M., Solazzo, E., Guizzardi, D. et al. Food systems are responsible for a third of global anthropogenic GHG emissions. Nat Food 2, 198–209 (2021). https://doi.org/10.1038/s43016-021-00225-9.
• Springmann, M., Clark, M., Mason-D’Croz, D. et al. Options for keeping the food system within environmental limits. Nature 562, 519–525 (2018). https://doi.org/10.1038/s41586-018-0594-0
• Xu, X., Sharma, P., Shu, S. et al. Global greenhouse gas emissions from animal-based foods are twice those of plant-based foods. Nat Food 2, 724–732 (2021). https://doi.org/10.1038/s43016-021-00358-x.
• Stehfest, E., Bouwman, L., van Vuuren, D.P. et al. Climate benefits of changing diet. Climatic Change 95, 83–102 (2009). https://doi.org/10.1007/s10584-008-9534-6.
• Steinfeld H, Gerber P, Wassenaar T, Castel V, Rosales M, De Haan C. (2006). Livestock's Long Shadow: Environmental Issues and Options. Rome, Italy: FAO. https://www.fao.org/4/a0701e/a0701e00.htm.}

According to the Institute for Health metrics and evaluation, three of the top 15 risk factors for early death in 2021 were dietary risk factors: high sodium intake, low fruit intake, and low whole grain intake (IHME 2025). Poor diets are a major risk factor for non-communicable diseases and responsible for 11 million deaths and 255 million disability-adjusted life-years (DALYs) worldwide (GBD 2017).

Consumption of fruits and vegetables has many benefits throughout the life-cycle including better growth in children and a longer life. Diets rich in fruits and vegetables can lower one's risk of heart disease, diabetes, and obesity while improving immunity and gut health. Worldwide, we consume only two thirds of this recommended amount (Afshin et al., 2019), with considerable variation across countries.

A study by Stanaway et al. (2022) found that increasing vegetable consumption from zero to 306–372 g daily was associated with:

• 23.2% decline in the risk of ischemic stroke

• 22.9% decline in the risk of ischemic heart disease

• 15.9% decline in the risk of hemorrhagic stroke

• 28.5% decline in the risk of esophageal cancer"

In 2019, The EAT Lancet Commission Willet et al. (2019) proposed a healthy and sustainable diet (i.e., the “Planetary Health Diet”, PHD), which recommends drastically reduced intake of meat and added sugar, and increased intake of fruits, vegetables, and legumes (Willet et al. 2019).

A Planetary Health Diet (PHD) is linked to a 30% lower risk of premature death and a reduced likelihood of developing cancer, heart disease, and lung disease (Bui et al., 2024). In contrast, high consumption of red and processed meat has been associated with an increased risk of various cancers, including colorectal, colon, lung, and renal cell cancer (Farvid et al., 2021). Unprocessed red meat has been linked to a higher risk of stroke (de Medeiros et al., 2022), while processed meat consumption is associated with an increased risk of diabetes and coronary heart disease (Micha et al., 2012). Additionally, diets high in ultra-processed foods have been connected to poorer cardiovascular health, cerebrovascular disease, depression, and a higher risk of all-cause mortality (Pagliai et al., 2020).

References:
^{• Afshin, Ashkan et al. (2017) Health effects of dietary risks in 195 countries, 1990–2017: a systematic analysis for the Global Burden of Disease Study The Lancet, Volume 393, Issue 10184, 1958 - 1972. https://doi.org/10.1016/S0140-6736(19)30041-8.
• Bui, Linh P et al. (2024) "Planetary Health Diet Index and risk of total and cause-specific mortality in three prospective cohorts" The American Journal of Clinical Nutrition, Volume 120, Issue 1, 80 - 91. https://ajcn.nutrition.org/article/S0002-9165(24)00389-7/abstract.
• de Medeiros, G. C. B. S., Mesquita, G. X. B., Lima, S. C. V. C., Silva, D. F. de O., de Azevedo, K. P. M., Pimenta, I. D. S. F., … Piuvezam, G. (2022). Associations of the consumption of unprocessed red meat and processed meat with the incidence of cardiovascular disease and mortality, and the dose-response relationship: A systematic review and meta-analysis of cohort studies. Critical Reviews in Food Science and Nutrition, 63(27), 8443–8456. https://doi.org/10.1080/10408398.2022.2058461.
• Guasch-Ferré and Willet (2021) The Mediterranean diet and health: a comprehensive overview. https://onlinelibrary.wiley.com/doi/full/10.1111/joim.13333.
• Farvid, M.S., Sidahmed, E., Spence, N.D. et al. Consumption of red meat and processed meat and cancer incidence: a systematic review and meta-analysis of prospective studies. Eur J Epidemiol36, 937–951 (2021). https://doi.org/10.1007/s10654-021-00741-9.
• GBD 2017 Diet Collaborators. Health effects of dietary risks in 195 countries, 1990-2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet. 2019 May 11; 393(10184): 1958-1972. https://doi.org/10.1016/S0140-6736(19)30041-8.
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• Micha, R., Michas, G. & Mozaffarian, D. Unprocessed Red and Processed Meats and Risk of Coronary Artery Disease and Type 2 Diabetes – An Updated Review of the Evidence. Curr Atheroscler Rep14, 515–524 (2012). https://doi.org/10.1007/s11883-012-0282-8.
• Pagliai G, Dinu M, Madarena MP, Bonaccio M, Iacoviello L, Sofi F. Consumption of ultra-processed foods and health status: a systematic review and meta-analysis. British Journal of Nutrition. 2021;125(3):308-318. https://doi.org/10.1017/S0007114520002688.
• Stanaway, J.D., Afshin, A., Ashbaugh, C. et al. Health effects associated with vegetable consumption: a Burden of Proof study. Nat Med28, 2066–2074 (2022). https://doi.org/10.1038/s41591-022-01970-5.
• Willett, Walter, Johan Rockström, Brent Loken, Marco Springmann, Tim Lang, Sonja Vermeulen, Tara Garnett, et al. 2019. ‘Food in the Anthropocene: The EAT–Lancet Commission on Healthy Diets from Sustainable Food Systems’. The Lancet 393 (10170): 447–92. https://doi.org/10.1016/S0140-6736(18)31788-4.}

The food system is responsible for a third of global anthropogenic greenhouse gas (GHG) emissions (Crippa et al. 2021). Reducing the share of animal-based proteins in diets as well as reducing food waste play an important role in reducing food system emissions (Bodirsky 2020, Clark 2020). Dietary shifts in line with the Planetary Health Diet (PHD) increase the feasibility of a 1.5°C pathway (Humpenöder et al. 2024). According to Humpenöder et al. 2024, such a dietary shift leads to substantial reductions in GHG emissions (especially methane) from the agriculture, forestry and other land use (AFOLU) sector. Consequently, with a shift of global dietary patterns towards a PHD, the same climate outcome can be achieved with a lower GHG price, less need for carbon dioxide removal (CDR). As such dietary change can reduce the costs of climate change mitigation substantially (Stehfest et al. 2009, Humpenöder et al. 2024). This also alleviates the pressure on food expenditure (Humpenöder et al. 2024).

References:
^{• Clark, M. A., Domingo, N. G. G., Colgan, K., Thakrar, S. K., Tilman, D., Lynch, J., Azevedo, I. L., & Hill, J. D. (2020). Global food system emissions could preclude achieving the 1.5° and 2°C climate change targets. Science, 370(6517), 705–708. https://doi.org/10.1126/science.aba7357.
• Crippa, M., Solazzo, E., Guizzardi, D. et al. Food systems are responsible for a third of global anthropogenic GHG emissions. Nat Food 2, 198–209 (2021). https://doi.org/10.1038/s43016-021-00225-9.
• Humpenöder, Florian, Alexander Popp, Leon Merfort, Gunnar Luderer, Isabelle Weindl, Benjamin Leon Bodirsky, Miodrag Stevanović, et al. 2024. ‘Food Matters: Dietary Shifts Increase the Feasibility of 1.5°C Pathways in Line with the Paris Agreement’. Science Advances. https://doi.org/10.1126/sciadv.adj3832.
• Stehfest, E., Bouwman, L., van Vuuren, D.P. et al. Climate benefits of changing diet. Climatic Change 95, 83–102 (2009). https://doi.org/10.1007/s10584-008-9534-6.}

A dietary shift towards more plant-based diets offers multiple environmental benefits beyond just reducing greenhouse gas emissions. It can decrease the pressure on land resources, conserve freshwater, and lessen the pollution of ecosystems through reduced nitrogen and phosphorus inputs (Springmann et al. 2018).

Shifting from animal products to more plant-based foods can substantially reduce the demand for cropland. Currently, the livestock sector occupies about 2/3 of global agricultural land for grazing, and more than 1/3 of global cropland is used for the production of animal feed, while animal based products only account for about 37% of global protein intake (Poore and Nemecek, 2018). Plant-based diets that directly consume grains, legumes, fruits, and vegetables generally require less land per unit of calorie or protein produced. Reduced pressure on land can slow down deforestation and mitigate biodiversity loss, and even free land for other environmental purposes (Steinfeld et al., 2006).

Similarily, animal based products have a substantially higher freshwater use per kilogram of product than plant-based foods, driven by the demand for feed, which accounts for 98% of the livestock sectors total water footprint (Mekonnen and Hoekstra, 2012). For example, the production of one kilogram of beef on average uses over 15 thousand litre of water (Mekonnen and Hoekstra, 2012). The lower demand for feed in plant-based diets can also contribute to a substantial reduction in the application of fertilizers, which – together with the decrease in animal waste – can mitigate pollution of aquatic and terrestrial ecosystems through nitrogen and phosphorus run-off (Springmann et al., 2018).

References:
^{• Springmann, M., Clark, M., Mason-D’Croz, D. et al. Options for keeping the food system within environmental limits. Nature 562, 519–525 (2018). https://doi.org/10.1038/s41586-018-0594-0.
• J. Poore, T. Nemecek, Reducing food’s environmental impacts through producers and consumers.Science360,987-992(2018). https://doi.org/10.1126/science.aaq0216.
• Steinfeld H, Gerber P, Wassenaar T, Castel V, Rosales M, De Haan C. (2006). Livestock's Long Shadow: Environmental Issues and Options. Rome, Italy: FAO. https://www.fao.org/4/a0701e/a0701e00.htm.
• Mekonnen, M.M., Hoekstra, A.Y. A Global Assessment of the Water Footprint of Farm Animal Products. Ecosystems 15, 401–415 (2012). https://doi.org/10.1007/s10021-011-9517-8.}

While plant-based diets are sometimes perceived as more expensive than the common omnivorous diets due to the role of expensive novel meat substitutes and higher costs of fruits and vegetables, research shows that a whole food, plant-based diet can be even cheaper than a typical diet (Pais et al. 2022). This is supported by studies using survey data from the US (Lusk et al. 2016) and Portugal (Pais et al. 2022) and a modelling study using regionally comparable food prices from 150 countries (Springmann et al. 2021).

In this modeling study, Springmann et al. (2021) estimated the costs of diets across 150 countries by combining data on food demand for various dietary patterns with commodity price estimates from different years. In high- and upper-middle-income regions, healthy and sustainable diets are found to be on average 22-34% lower in cost compared to current diets (Springmann et al. 2021). Vegetarian and vegan diets tend to be the most affordable, while pescatarian diets are the least affordable (Springmann et al. 2021). In lower-middle-income and low-income countries, adopting healthy diets increases costs by 18–29%. However, combining this shift with reduced food waste, socioeconomic development, and accounting for climate and health-related costs improves affordability. By 2050, these measures could lower diet costs by 25–29% in low-income countries and up to 37% globally (Springmann et al. 2021).

References:
^{• Springmann, Marco, Michael A Clark, Mike Rayner, Peter Scarborough, and Patrick Webb. 2021. ‘The Global and Regional Costs of Healthy and Sustainable Dietary Patterns: A Modelling Study’. The Lancet Planetary Health 5 (11): e797–807. https://doi.org/10.1016/S2542-5196(21)00251-5.
• Pais, Daniel Francisco. 2022. ‘The Cost of Healthier and More Sustainable Food Choices: Do Plant-Based Consumers Spend More on Food?’ https://doi.org/10.1186/s40100‑022‑00224‑9.
• Lusk, Jayson L., and F. Bailey Norwood. 2016. ‘Some Vegetarians Spend Less Money on Food, Others Don’t’. Ecological Economics 130 (October):232–42. https://doi.org/10.1016/j.ecolecon.2016.07.005.}

Transforming food demand requires moving beyond individual choices and toward systemic change. Implementing policies that create supportive food environments—such as nudging strategies, increasing the availability of healthy, affordable, and climate-friendly foods, and applying targeted pricing policies—can significantly influence both individual food choices and broader societal shifts (Garnett et al., 2019, 2020, 2021; Meier et al., 2022). Public food providers play a crucial role in this transformation (Marteau et al., 2021). Canteens, for example, can contribute to climate change mitigation not only by adopting more sustainable food procurement practices but also by shaping societal norms and encouraging healthier, more sustainable dietary choices (Lambrecht et al., 2023).

Possible strategies for canteens to contribute to a food system transformation are:

• Offer more vegetarian options: A large-scale observational and experimental field study conducted in three cafeterias at an English university showed that by doubling the proportion of vegetarian meal options from 25% to 50%, researchers found that vegetarian sales increased by 41% to 79%, with the largest effect among those who previously ate the least vegetarian food (Garnett et al. 2019). The findings suggest that increasing vegetarian availability is an effective, low-impact strategy for promoting sustainable diets without reducing overall meal sales.

• Adjust the food offering such that the healthy option is the default. A study by Meier et al. (2022) finds that "green defaults" are effective in reducing meat consumption, primarily through mechanisms of endorsement (implying the default is recommended) and effort (making alternative choices require more effort). The impact of defaults is influenced by factors such as how invasive they are, how alternatives are presented, and the study setting

• Making healthy vegan/vegetarian food options relatively cheaper (i.e., small increases in price for meat option and small decrease in price for vegetarian option): An experiment at the  University of Cambridge cafeteria suggests that modest price adjustments can encourage vegetarian choices, particularly among those already inclined toward plant-based meals (Garnett et al. 2021)

References:
^{• Attwood S, Voorheis P, Mercer C, Davies K, Vennard D (2020) Playbook for guiding diners toward plantrich dishes in food service. World Resources Institute. https://www.wri.org/research/playbook-guiding-diners-toward-plant-rich-dishes-food-service.
• Garnett EE, Balmford A, Sandbrook C, Pilling MA, Marteau TM (2019) Impact of increasing vegetarian availability on meal selection and sales in cafeterias. Proc Natl Acad Sci 116:20923–20929. https:// doi.org/10.1073/pnas.1907207116.
• Garnett EE, Marteau TM, Sandbrook C, Pilling MA, Balmford A (2020) Order of meals at the counter and distance between options affect student cafeteria vegetarian sales. Nat Food 1:485–488. https:// doi.org/10.1038/s43016-020-0132-8.
• Garnett, Emma E., Andrew Balmford, Theresa M. Marteau, Mark A. Pilling, and Chris Sandbrook. 2021. ‘Price of Change: Does a Small Alteration to the Price of Meat and Vegetarian Options Affect Their Sales?’ Journal of Environmental Psychology 75 (June):101589. https://doi.org/10.1016/j.jenvp.2021.101589.
• Lambrecht, N. J., Hoey L., Bryan, A., Heller, M. and Jones, A. D. (2023). Limiting red meat availability in a university food service setting reduces food-related greenhouse gas emissions by one-third. Climate Change. 176(6), 67. https://doi.org/10.1007/s10584-023-03543-y.
• Marteau TM, Chater N, Garnett EE (2021) Changing behaviour for net zero 2050. BMJ 375:n2293. https://doi.org/10.1136/bmj.n2293.
• Meier, Johanna, Mark A. Andor, Friederike C. Doebbe, Neal R. Haddaway, Lucia A. Reisch, (2022). “Review: Do green defaults reduce meat consumption?”, Food Policy, 110(2022), https://doi.org/10.1016/j.foodpol.2022.102298.}