Can a diet that's good for the planet reduce your risk of dying from disease?

A diet promoting plant-based protein to help the environment now has a more human argument: It may lower your risk of dying from several major diseases. 

"It wasn't just one cause of death. It was right across the board," said Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health. 

Willett co-authored a new study looking at the Planetary Health Diet (PHD) — which he helped develop in 2019 as part of the EAT-Lancet Commission — and its effects on mortality. The diet advises plant-based proteins such as nuts and legumes, more fruit and vegetable consumption as well as healthy, unsaturated fats — while decreasing animal-based sources of protein and added sugars. 

The new study, published in the peer-reviewed American Journal of Clinical Nutrition, looked at decades of diet data from more than 200,000 health-care workers in the United States. It scored how closely participants' eating habits compared to the Planetary Health Diet. The closer they ate like the PHD — for example, eating more nuts and less red meat — the greater the benefit. 

"Every major cause of mortality was lower," Willett said, "Including heart disease, cancer, neurodegenerative conditions like Alzheimer's disease, Parkinson's disease and a strong benefit for [respiratory] mortality." 

Willett also noted that the top 10 per cent of participants who followed the diet saw a 30 per cent lower risk of dying from all causes.

The death data was obtained from the more than 54,000 participants who died over the course of the study period. 

Kathryn Bradbury, a senior research fellow in the School of Population Health at the University of Auckland, called the research comprehensive, and said it accounted for outside factors.  

"They also looked at other things that the people were doing in terms of their exercise and their smoking habits," says Bradbury, who was not involved in the study. She highlighted the specific foods in the study that had more of an impact. 

"If you had eaten lots of whole grains, lots of nuts and lots of healthy fats like olive oil and sunflower oil," Bradbury told CBC News from Auckland, "they were the most important things in terms of reducing your risk of death."

She added that reducing red meat was also important in their analysis. 

For Toronto-based chef, author and food activist Joshna Maharaj, the study is both obvious and important. 

"It's beautiful, fundamental, basic wisdom," Maharaj said, calling it more academic support of what sustainability advocates have long talked about.

But she stresses it's not just about reducing certain foods like red meat — it's about growing the food more organically.