Planetary Health Diet reduces premature death risk and carbon emissions, Harvard study finds

13 Jun 2024 --- A recent study conducted by researchers from Harvard TH School of Public Health, US, found that people with a higher adherence to the Planetary Health Diet (PHD) — also known as the planetary or planetarian diet — had a 30% lower risk of premature death compared to those with the lowest adherence. PHD is a flexitarian diet created by the EAT-Lancet Commission in 2019. The current study developed a PHD Index (PHDI) to quantify adherence to the EAT-Lancet reference diet.

“Our study is noteworthy given that the US 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 US Dietary Guidelines,” says Walter Willet, professor, epidemiology and nutrition at Harvard TH School of Public Health and corresponding author of the study.

“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 well-being of every person on earth.”

Earlier this month, the International Food Policy Research Institute released its 2024 Global Food Policy Report, underscoring the importance of transforming complex global food systems to foster sustainable, healthy diets across all demographics. The report aims to be a beacon of practical information amid growing challenges of unhealthy diets, malnutrition and climate change.

Dietary patterns make a difference
The study, published in the American Journal of Clinical Nutrition, is the first large study to directly evaluate the impacts of adherence to the recommendations in the landmark EAT-Lancet report. Their goal was to assess associations between PHDI and total and cause-specific mortality in three prospective cohorts of males and females in the US.

The PHD consists of a variety of minimally processed plant foods while allowing modest meat and dairy consumption. A healthy, sustainable diet can substantially lower a person’s risk of premature death and environmental impact. 

“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,” says Willet.According to a new study by Harvard TH Chan School of Public Health researchers, the Planetary Health Diet is a benchmark for health and sustainability. 

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. The participants had no chronic diseases and completed dietary questionnaires every four years for up to 34 years. Their diets were scored based on consuming 15 food groups, including whole grains, vegetables, poultry and nuts, quantifying adherence to 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 the PHD dietary pattern.

Last month, the European Food Information Council released recommendations for nutrition communication based on a new study exploring “Which messages about healthy and sustainable eating resonate best with consumers with low socioeconomic status?”

Favorable carbon footprint 
The researchers found that people with the highest adherence to the PHD had a substantially lower environmental impact than those with the lowest, including 29% lower greenhouse gas (GHG) emissions, 21% lower fertilizer needs and 51% lower cropland use. 

According to the researchers, other studies found that diets emphasizing plant-based foods over animal-sourced foods could benefit human and planetary health. Many used one-time dietary assessments, which produce weaker results than looking at diets over a long period of time. They note that land use reduction is an important facilitator of reforestation, which reduces climate-driven GHGs.

Meanwhile, the World Wildlife Fund headquarters in the Netherlands released a groundbreaking research report about the connection between planetary sustainability and dietary choices based on a study using the Netherlands Nutrition Center’s Wheel of Five and the global EAT-Lancet menu for 2050.

By Inga de Jong