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Confirmed. Most robust evidence yet that plant-based diets protect both human and planetary health  

Largest study of its kind shows the co-benefits to environment and health of eating less meat and more plants.
June 14, 2024

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People who follow a diet rich in plants cut their mortality risk by almost a third, while simultaneously slashing the climate impact of their food by a similar amount. These results come from the largest study ever to analyze the health and environmental impacts of the widely-publicized EAT-Lancet Planetary Health Diet

Launched in 2019, the EAT-Lancet Commission brought together reams of research to determine what would be the best way for us to eat on a global scale, to limit the environmental impacts of farming and food. The Commission came up with a diet rich in fruits, vegetables, whole grain and plant-sourced proteins, and lower in—but crucially not excluding—animal-sourced products like meat and dairy milk. That became known as the Planetary Health Diet. 

Until now, however, the benefits of this diet have been explored mainly on a small scale. The new study takes it up a notch. “This is by far the longest term, large study in actual people to look at both the human and planetary health benefits of the Planetary Health Diet,” says Walter Willett, the Fredrick John Stare professor of epidemiology and nutrition at the Harvard School of Public Health, and lead author on the research.

His new paper, published in The American Journal of Clinical Nutrition, relied on three pre-existing datasets that drew dietary information from over 200,000 American nurses over a 34-year period between 1986 to 2019. All participants were disease-free when the surveying started, and were required to complete a questionnaire every four years on the makeup of their diets. 


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What would happen if just 54 wealthy nations adopted the EAT-Lancet planetary health diet?


To evaluate this vast trove of data, Willett and colleagues first selected 15 indicator foods that captured the span of dietary impacts, including whole fruits, vegetables, and nuts on the lower-impact end; and red meat, processed meat, and dairy on the higher-impact end. Then, they used these foods to develop an index that allowed them to score the nurses’ dietary surveys by how closely they aligned with the EAT-Lancet suggested Planetary Health Diet. Using a lifecycle-analysis, they estimated the environmental impacts of each reported diet according to those 15 indicator foods.

Because the study also recorded a varied set of health outcomes for the participants—everything ranging from cancer to diabetes, heart disease, lung disease, and neurodegenerative problems—this allowed Willett and team to correlate participants’ dietary trends with their health over the 34-year period. 

Their analysis left little doubt that those who eat diets richer in plants are also healthier, as well as having a lower environmental footprint. In fact, in the top 10% of participants, whose plant-heavy diets most closely matched the Planetary Health Diet, the risk of premature death due to disease was 23% lower than those in the bottom 10% of the survey. These plant-keen participants showed a 14% lower risk of death from cardiovascular disease, a 10% lower risk of death from cancer, a 28% reduced risk of death from neurodegenerative conditions, and strikingly, a 47% lower death risk from respiratory disease.

Meanwhile, the environmental gains of eating more plants were striking too: their diets produced 29% less in the way of greenhouse gas emissions, required 21% less fertilizer, and 51% less cropland area compared to those whose diets scored lowest in the index. The reduced land use could bring significant further climate gains, if it is turned over to wild habitat again, which would lock in more carbon via new vegetation and undisturbed soils. 

The study only showed a correlation, not a causation, between plant-focused diets and better health, which means it’s possible that other factors like exercise and smoking habits will explain the healthier outcomes of some participants. Although, the researchers say they did take these factors into account.

And besides, the study backs up a connection that many other studies have shown between greener diets and healthier outcomes, and it does so on an unprecedented scale—with clear environmental benefits to boot. 

Overall, the new research builds the case for plant-focused diets as an approach with immense power to help relieve poor health and environmental decline. And critically, eating better for human and planetary health doesn’t require huge changes or sacrifice, which could help make it easier for most people to accept, Willett says. “The Planetary Health Diet, which is plant-forward but can include modest amounts of meat and dairy foods, provides a huge double win: great for the health of both people and planet.”

Willett et. al. “Planetary Health Diet Index and risk of total and cause-specific mortality in three prospective cohorts.The American Journal of Clinical Nutrition. 2024.


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