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-reviewedAmerican Journal of Clinical Nutrition, looked at decades of diet data from more than 200,000 health-care workersin 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.

Specific foods were associated with lower risk

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.

Making a change

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.

"There is an ecological way to consume meat," said Maharaj. "You may eat less of it and pay more for it, but raising and eating animals can be part of a system that works."

Maharaj says current meat production is industrial andtaxing on the environment, through both the chemicals used and the land used to support factory farming.

Farmers market or big box grocery chain? Guess the origin of these food items

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Duration 9:51

Can you tell the difference between local produce and a grocery store import? Test your food knowledge with Samira Mohyeddin, host of CBC Radio series Unforked, and Toronto chef and author Joshna Maharaj.

She says Canadians looking to make a change can start by looking in their fridge and learning about their own consumption patterns.

"Don't worry about making magic change," Maharaj said.

Plates and policies

The good news for Canadians is that the country's revamped food guide in 2019 already encourages more plant-based proteins as well as limiting processed foods and sugary drinks.

"Canada's food guide is largely consistent with a sustainable dietary pattern," says Benot Lamarche, scientific director of Laval University's NUTRISS centre, and who recently authored a paper that compared the guide to the PHD.

But a challenge remains in how to convey an ideal plate of food to people. For example, Canada's food guideshows a tidy quarter devoted to general proteins, telling people how much versus what kinds of protein.

"We need protein, but total protein is not a good indicator of how healthy we are eating," said Lamarche."The source of the protein is a better marker of our diet quality."

Beyond just healthy eating, a sustainable diet needsto also consider affordability, cultural relevance and whether it's truly good for the environment, Lamarche stressed.

Can a diet really save the planet?

The new study also found that adhering to the PHD came with a lower environmental impact, based on calculations that foods in this diet would emit fewer greenhouse gases, require less water, fertilizer and crop land.

"That's huge," Willett told CBC News from Cambridge, Mass., "Because it really means that we could allow some of our cultivated land to go back to forest which would definitely help stabilize the global climate situation."

Climate change, driven largely by the burning of fossil fuels, is also exacerbated by agricultural emissions, which includemethane, a shorter-living but more potent greenhouse gas. A negative feedback loop occurs as food production is then threatened by drought and other extreme weather events, strengthened and lengthened by climate change.

According to Our World in Data's analysis of UN figures, an estimated 80 per centof agricultural land on the planet is used for grazing and growing feed for livestock.

"If on a population level, everyone reduced their intake of animal-sourced foods," said Bradbury, "It would be much more efficient, because we'd be using that land to directly grow plant crops that we would eat."

Willett says addressing our food's impact on the climate is urgent.

"It is frightening and is unique because it's not linear, it's accelerating. And we're hitting tipping points that are going to be irreversible."