Harvard Study: Planet-Friendly Diet Cuts Premature Death Risk by Nearly a Third

A groundbreaking Harvard study reveals that the healthiest diet for the planet may also be the best for human longevity, potentially reducing the risk of premature death by nearly a third.

The study, published last week in The American Journal of Clinical Nutrition, set out to evaluate the health impacts of the planetary health diet—a climate-friendly diet that emphasizes fruits, vegetables, and whole grains, and minimizes red meat and other foods with a high carbon footprint.

Researchers pooled data from three long-term, large-scale studies that followed roughly 200,000 participants over the course of decades, periodically surveying them about their eating habits and health. They scored each participant’s diet based on environmental impact. All participants were free of major chronic diseases at the outset. After reviewing health outcomes over time, the researchers identified a striking association: The more eco-friendly a participant’s diet was, the less likely they were to die prematurely of any cause. Those whose diets scored in the top 10% in terms of sustainability were 30% less likely to die prematurely than those who scored in the bottom 10%.

“For every major cause of death we looked at, there was a lower risk in people with better adherence to the planetary health diet,” says Walter C. Willett, a lead author on the new study and a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. “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 2019, an international team of 37 scientists released the EAT–Lancet report—a comprehensive assessment, with regards to human health and environmental sustainability, of the way we eat and produce food. The landmark report concluded that our current dietary and food production patterns are incompatible with the long-term survival of our species, and that in order to feed the 10 billion people (the expected population in 2050), a major shift is required away from red meat and toward vegetables, grains, legumes, and nuts. The report put forward a “planetary health diet,” a flexitarian diet that is largely plant-based but can optionally include modest amounts of fish, meat, and dairy foods. If widely adopted, the planetary health diet would reduce greenhouse gases by 50% by 2050, while also reducing rates of chronic disease in humans, according to the EAT–Lancet Commission’s projections.

Fruits, vegetables, and whole grains require significantly less land to produce and generate significantly fewer greenhouse gases than meat. A 2019 review found that the climate-altering carbon emissions from a single gram of protein from beef are at least 7.5 times higher than those associated with a gram of protein from plant sources.

“Shifting how we eat can help slow the process of climate change,” says Willett. “And what’s healthiest for the planet is also healthiest for humans.”

To learn more about a whole-food, plant-based diet, visit our Plant-Based Primer. For meal-planning support, check out Forks Meal Planner, FOK’s easy weekly meal-planning tool to keep you on a healthy plant-based path.