People who follow a healthy, sustainable diet known as the Planetary Health Diet (PHD) may significantly reduce their risk of premature death while also minimizing their environmental impact, according to a groundbreaking study led by researchers at the Harvard T.H. Chan School of Public Health. The study, set to be published online June 10 in The American Journal of Clinical Nutrition, is the first large-scale investigation to directly assess the impacts of adhering to the recommendations outlined in the landmark 2019 EAT-Lancet report.
The PHD, as defined in the report, emphasizes a wide variety of minimally processed plant foods while allowing for modest consumption of meat and dairy products. “Climate change has our planet on track for ecological disaster, and our food system plays a major role,” said Walter Willett, professor of epidemiology and nutrition and the study’s corresponding author. “Shifting how we eat can help slow the process of climate change. And what’s healthiest for the planet is also healthiest for humans.”
Long-Term Dietary Data Strengthens Findings
Unlike previous studies that relied on one-time dietary assessments, the Harvard researchers used health data spanning up to 34 years 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, who were free of major chronic diseases at the start of the study, completed dietary questionnaires every four years. Their diets were scored based on intake of 15 food groups, including whole grains, vegetables, poultry, and nuts, to quantify adherence to the PHD.
The study found that participants in the top 10% of adherence to the PHD had a 30% lower risk of premature death compared to those in the lowest 10%. Moreover, every major cause of death, including cancer, heart disease, and lung disease, was lower with greater adherence to this dietary pattern.
Planetary Health Diet Linked to Lower Environmental Impact
In addition to the health benefits, the researchers discovered that those with the highest adherence to the PHD had a substantially lower environmental impact than those with the lowest adherence. This included 29% lower greenhouse gas emissions, 21% lower fertilizer needs, and 51% lower cropland use.
The researchers emphasized the importance of land use reduction as a facilitator of re-forestation, which is considered 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,” Willett said. “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.”
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.
