Harvard Study Reveals: Planetary Health Diet Can Extend Your Life and Save Earth Too

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A study by Harvard T.H. Chan School of Public Health highlights the dual benefits of the Planetary Health Diet (PHD), which not only reduces the risk of premature death by up to 30% but also significantly decreases environmental impacts. The PHD, which advocates for a varied diet of minimally processed plant foods with limited meat and dairy, is shown to lower greenhouse gas emissions, fertilizer needs, and cropland use, demonstrating the deep connection between dietary choices and both human and planetary health.

Adhering to the Planetary Health Diet significantly reduces the risk of premature death and environmental impact, including lowered rates of major diseases and reduced greenhouse gas emissions and land use.

According to a new study from Harvard T.H. Chan School of Public Health, adopting a healthy, sustainable diet, as outlined in the 2019 EAT-Lancet report, can significantly reduce both the risk of premature death and environmental impact. This landmark study is the first to directly assess the effects of following the dietary guidelines proposed in the report, which recommends a diverse intake of minimally processed plant foods while permitting limited amounts of meat and dairy. The researchers refer to this recommended diet as the Planetary Health Diet (PHD).

The study was recently published in The American Journal of Clinical Nutrition.

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

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 researchers used health data from more than 200,000 women and men enrolled in the 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.

Health and Environmental Benefits of the PHD

The study found that the risk of premature death was 30% lower in the top 10% of participants most closely adhering to PHD 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.

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.

The researchers noted that land use reduction is particularly important as a facilitator of re-forestation, which is seen as an effective way to further reduce levels of greenhouse gases that are driving climate change.

“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 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.”

Reference: “Planetary Health Diet Index and risk of total and cause-specific mortality in three prospective cohorts” by Linh P Bui, Tung T Pham, Fenglei Wang, Boyang Chai, Qi Sun, Frank B Hu, Kyu Ha Lee, Marta Guasch-Ferre and Walter C Willett, 10 June 2024, The American Journal of Clinical Nutrition.
DOI: 10.1016/j.ajcnut.2024.03.019

Other Harvard Chan School authors included Linh Bui, Fenglei Wang, Qi Sun, Frank Hu, Kyu Ha Lee, and Marta Guasch-Ferre.

The study was funded by National Institutes of Health (NIH) research grants UM1 CA186107, P01 CA87969, R01 HL034594, U01 CA176726, U01 CA167552, R01 HL035464, R01 DK120870, and R01 DK126698.

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