In a new study published in the journal Lancet Planetary Health, researchers characterized the health and environmental impacts associated with high versus low scores on various plant-rich dietary indices in a U.S. cohort study. These researchers found that participants in the highest alternative healthy eating index-2010 (AHEI) and healthy plant-based diet index (PDI) score quintiles had a reduced risk of cardiovascular disease; reduced greenhouse gas emissions; and reduced use of cropland, irrigation water, and nitrogenous fertilizer. In contrast, participants in the highest unhealthy PDI score quintile had an increased risk of cardiovascular disease, and their diets required more cropland and fertilizer, compared with those in the lowest unhealthy PDI score quintile (Musicus et al., 2022).
“The unhealthy PDI emphasizes consumption of plant-based foods that are rich in refined grains and added sugars; diets with higher unhealthy PDI scores are associated with a higher risk of coronary heart disease compared with plant-based diets that are rich in whole grains, legumes, nuts, fruits, and vegetables, which have higher scores on the healthy PDI.” The alternative healthy eating index (AHEI) emphasizes plant-based foods and provides higher scores for healthy plant-based foods, and for some animal-sourced foods such as fish. Diets with higher AHEI scores are associated with a lower risk of major chronic disease (Musicus et al., 2022).
“Using data from the Nurses’ Health Study II, the researchers analyzed the food intakes of more than 65,000 qualifying participants, and examined their diets’ associations with health outcomes, including relative risks of cardiovascular disease, and with environmental impacts” (Harvard T.H. Chan School of Public Health, 2022). “Participants who consumed healthy plant-based diets had lower cardiovascular disease risk, and those diets had lower greenhouse gas emissions and use of cropland, irrigation water, and nitrogenous fertilizer than diets that were higher in unhealthy plant-based and animal-based foods. Participants who ate unhealthy plant-based diets experienced a higher risk of cardiovascular disease, and their diets required more cropland and fertilizer than diets that were higher in healthy plant-based and animal foods. The findings also reinforced earlier studies showing that diets higher in animal-based foods, especially red and processed meat, have greater adverse environmental impacts than plant-based diets” (Harvard T.H. Chan School of Public Health, 2022). Participants with diets in the highest quintiles of greenhouse gas emissions, land use, fertilizer inputs, and water use generally had higher body mass indices (BMIs) and lower levels of physical activity (Musicus et al., 2022).
The food groups that contributed the most to greenhouse gas emissions associated with participants’ dietary intake were all animal-based and included red and processed meat (31.0% of all participants’ dietary greenhouse gas emissions), dairy (13.2%), poultry (9.3%), and fish (5.6%). Plant-based food groups with the highest greenhouse gas emissions based on participant intakes included fruit juice (4.9%), vegetables (4.6%), and fruit (3.2%). Red and processed meat also contributed the most to use of cropland (59.4% of all cropland use for participants’ diets), irrigation water (26·3%), and fertilizer (25.0%). Dairy was responsible for 8.6% of use of cropland, 6·6% of irrigation water, and 8.5% of fertilizer. Aside from meat (26.3%) and dairy (6.6%), vegetable intake was responsible for 24.6% of irrigation water use (with fruit contributing 6·5% and nuts 5·1% of total irrigation water use). Plant-based foods that were responsible for the highest fertilizer use were vegetables (11.4%), whole grains (6.6%), refined grains (5.1%), and fruit (4.0%) (Musicus et al., 2022).
As noted in a recent article published in Anthropocene Magazine, in the current study, there were “variable impacts across food types – such as farmed vegetables which promote human health but which have a large water footprint, in fact four times that of fruit. Fruit juices, meanwhile, had a surprisingly large greenhouse gas footprint—almost as large as fish—when compared to other foods. Sugar-sweetened beverages were linked to significant amounts of fertilizer use, more than potatoes, legumes and nuts. Similarly, whole grains needed large amounts of fertilizer, sitting just a couple of notches below the fertilizer footprint of dairy farming.” (Bryce, 2022). View Figure 1 below to see different foods’ contributions to greenhouse gas emissions, cropland needs, irrigation water needs, and fertilizer (Musicus et al., 2022).
Figure 1: Different foods’ contributions to greenhouse gas emissions, cropland needs, irrigation water needs, and fertilizer.
Based on these results, the authors concluded that, “Plant-based dietary patterns that are associated with better human health are also associated with better environmental health. Future US dietary guidelines should include consideration of environmental sustainability and recognize that the human and environmental health co-benefits or more sustainable diets, but also that not all plant-based diets confer the same health and environmental benefits” (Musicus et al., 2022).
Although sustainability was omitted from the 2020–25 DGA [Dietary Guidelines for Americans], the current findings suggest “that future DGAs could benefit from the incorporation of dietary sustainability; such a change could both educate consumers and influence tens of millions of Americans’ diets through updated standards in federal feeding programs. This recommendation is supported by the EAT-Lancet Commission’s 2019 report findings, which highlighted the need for a global food-system transformation to ensure that the world’s rapidly growing population can be fed healthy diets from sustainable food systems (Musicus et al., 2022).
In the large prospective cohort of EPIC (European Prospective Investigation into Cancer and Nutrition), with a follow-up of 14 years and more than 400, 000 participants, Laine et al. (2021) reported that, “Greenhouse gas emissions could be reduced up to 50% and land use levels reduced up to 62%, by eating foods that span a higher EAT–Lancet diet score compared to eating foods that comprise a lower EAT–Lancet diet score.” These authors also found that, “up to 63% of deaths and 39% of incident cancers could be prevented in a 20-year risk period by fully adopting the EAT–Lancet reference diet (ie, perfect adherence), compared to not adopting the diet.” EPIC consists of 23 study centers in ten European countries: Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden, and the UK (Laine et al., 2021).
Certain countries such as Denmark have already incorporated sustainability into their dietary guidelines. See below for a poster of Denmark’s climate-friendly dietary guidelines released in 2021.
The Official Danish Dietary Guidelines – good for health and climate. 2021. Available at: https://altomkost.dk/fileadmin/user_upload/altomkost.dk/Publikationsdatabase/De_officielle_Kostraad_2021/Danish_Official_Dietary_Guidelines_Good_for_Health_and_climate_2021_SCREEN_ENG.pdf
Harvard T.H. Chan School of Public Health, Harvard University. Healthy plant-based diets better for environment than less healthy plant-based diets. Press Release. November 10, 2022. Available at: https://www.hsph.harvard.edu/news/press-releases/healthy-plant-based-diets-better-for-the-environment-than-less-healthy-plant-based-diets/
Musicus AA, Wang DD, Janiszewski M, et al. Health and environmental impacts of plant-rich dietary patterns: a US prospective cohort study. Lancet Planet Health. 2022;6(11):e892-e900. doi: 10.1016/S2542-5196(22)00243-1.
Bryce M. Not all plant-based diets are equal… for health and the environment. Anthropocene Magazine. November 18, 2022. Available at: https://www.anthropocenemagazine.org/2022/11/not-all-plant-based-diets-are-equal-for-health-or-the-environment/?utm_source=rss&utm_medium=rss&utm_campaign=not-all-plant-based-diets-are-equal-for-health-or-the-environment&utm_source=rss&utm_medium=rss&utm_campaign=not-all-plant-based-diets-are-equal-for-health-or-the-environment
Laine JE, Huybrechts I, Gunter MJ, et al. Co-benefits from sustainable dietary shifts for population and environmental health: an assessment from a large European cohort study. Lancet Planet Health. 2021;5(11):e786-e796. doi: 10.1016/S2542-5196(21)00250-3.