Harvard Researchers: “Planet-friendly” Diet Promotes Human Longevity, Cuts GHG Emissions

Was Frances Moore Lappé ahead of her time when she wrote the bestseller, Diet for a Small Planet? The book, which has sold more than three million copies since it was first published in 1971, argued that industrial food production has a negative impact on the environment. Presenting a basic guide for a healthy diet along with recipes, Lappé’s groundbreaking book advocated for “environmental vegetarianism.”

Now, in time for the northern hemisphere’s extreme summer heat, researchers at Harvard University’s T.H. Chan School of Public Health suggest that a “Planetary Health Diet” (PHD) that emphasizes fruits, vegetables and whole grains, while allowing for modest consumption of meat and dairy products, reduces the risk of premature death in humans by nearly one third – while also reducing the release of greenhouse gases that are linked to global warming and climate change.

The study, published on June 10th, 2024, in The American Journal of Clinical Nutrition, found that the risk of premature death was 30% lower in the top 10% of participants most closely adhering to the Planetary Health Diet compared to those in the lowest 10%. Every major cause of death, including cancer, heart disease and lung disease, was lower with greater adherence to this dietary pattern, said the study’s authors.

“For every major cause of death we looked at, there was a lower risk in people with better adherence to the Planetary Health Diet,” Walter Willett, M.D., professor of epidemiology and nutrition and co-author of the study, said in a statement.

In addition, the researchers found that those with the highest adherence to the PHD had a substantially lower environmental impact than those with the lowest adherence, including 29% lower greenhouse gas emissions, 21% lower fertilizer needs, and 51% lower cropland use.

“Climate change has our planet on track for ecological disaster, and our food system plays a major role. Shifting how we eat can help slow the process of climate change. And what’s healthiest for the planet is also healthiest for humans,” Dr. Willet said.

The Harvard researchers noted that their work is the first large-scale study to directly evaluate the impacts of adherence to recommendations in the landmark EAT-Lancet report. Published in 2019, the report was the first full scientific review that brought together 37 world-leading scientists to ask the question, “Can we feed a future population of 10 billion people a healthy diet within planetary boundaries?”

While other studies have found that diets emphasizing plant-based foods over animal-sourced foods could have benefits for human and planetary health, most have used one-time dietary assessments, which produce weaker results than looking at diets over a long period of time, the authors noted.

As such, the researchers used health data from more than 200,000 women and men enrolled in Harvard’s Nurses’ Health Study I and II and the Health Professionals Follow-Up Study. Participants were free of major chronic diseases at the start of the study and completed dietary questionnaires every four years for up to 34 years. Participants’ diets were scored based on intake of 15 food groups—including whole grains, vegetables, poultry, and nuts—to quantify adherence to the PHD.

“Eating more whole plant foods, less animal foods, and less highly processed foods is better for people and planet alike,” David Katz, M.D., told CNN in a recent interview about the study. “In this paper, we see that same message amplified: adhering to a dietary pattern conducive to the health of the planet and sustainability is associated with meaningful reductions in all-cause mortality.” Katz is the founder of the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.

“Our study is noteworthy given that the U.S. Department of Agriculture has refused to consider the environmental impacts of dietary choices, and any reference to the environmental effects of diet will not be allowed in the upcoming revision of the U.S. Dietary Guidelines,” said Dr. Willett. “The findings show just how linked human and planetary health are. Eating healthfully boosts environmental sustainability—which in turn is essential for the health and wellbeing of every person on earth.”

In 2021, for the 50th anniversary of the publication of Diet for a Small Planet, Frances Moore Lappé wrote, “In 1970, I never imagined the impact of our diet on the looming life-and-death climate crisis. Nor that 40 years later my own daughter, Anna, would tackle this threat in Diet for a Hot Planet, enabling me to learn so much about the climate-food connection. If we achieve a societal shift toward plant-based diets, we can reduce greenhouse gas emissions from farming by as much as 70% by 2050, she noted.

Lappé added, “Worldwide, if those eating meat-centered diets simply moved to popular low-meat or no-meat fare – such as traditional Mediterranean or vegetarian cuisine – emissions could be reduced by an amount equal to the current greenhouse gas emissions of all cars, trucks, planes, trains and ships…More heartening news is that changes to farming and eating that benefit our Earth also enhance our health.”

Learn more:
Evaluating Population Diets and Planetary Health—Shining New Light
American Journal of Clinical Nutrition, June 10, 2024

Diet for a Hot Planet, by Anna Lappé, originally published in 2010

Diet for a Small Planet, by Francis Moore Lappé, originally published in 1971

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