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

A diet that promotes plant-based proteins to help the environment now has a more human argument: It can lower the risk of death from several serious diseases.

“It wasn’t just one cause of death. It was across the board,” said Walter Willett, professor of epidemiology and nutrition at the Harvard TH Chan School of Public Health.

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

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

“Every major cause of death was lower,” Willett said, “including heart disease, cancer, neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and a strong benefit for [respiratory] mortality.”

Willett also noted that the top 10 percent of participants who followed the diet saw a 30 percent lower risk of dying from any cause.

Death data were obtained from the more than 54,000 participants who died during the study period.

Specific foods were associated with a lower risk

Kathryn Bradbury, a senior research fellow at the University of Auckland’s School of Population Health, called the study comprehensive and said it took external factors into account.

“They also looked at other things 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 impact.

“If you ate a lot of whole grains, a lot of nuts and a lot of healthy fats like olive oil and sunflower oil,” Bradbury told CBC News from Auckland, “then these were the most important things in terms of reducing the risk of death.”

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

Three sample plates from the EAT-Lancet Commission’s Planetary Health Diet, with more plant-based protein sources, more vegetables and whole grains. (EAT-Lancet Committee)

Make a change

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

“It’s beautiful, fundamental wisdom,” Maharaj said, calling it more academic support for what sustainability advocates have long been talking about.

But she emphasizes that it’s not just about cutting back on certain foods, such as red meat, but about growing food more organically.

“There is an ecological way to consume meat,” Maharaj said. “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 and taxing on the environment, both due to the chemicals used and the land used to support factory farming.

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

“Don’t worry about making magical changes,” Maharaj said.

Records and policy

The good news for Canadians is that the country’s updated 2019 food guide already encourages more plant-based proteins and limits processed foods and sugary drinks.

“The Canadian Food Guide is largely consistent with a sustainable diet,” says Benoît Lamarche, scientific director of Laval University’s NUTRISS centre, and who recently wrote an article comparing the guide to the PHD.

Example of a healthy plate from the Canadian Food Guide.  Half the plate consists of fruits and vegetables, a quarter of whole grains and a quarter of proteins.
An example of an ideal, healthy plate from the Canadian Food Guide. (Canada Food Guide (2019))

But a challenge remains in conveying an ideal plate of food to people. For example, the Canadian Food Guide shows a neat section devoted to general proteins, telling people how much versus what types of protein.

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

In addition to just eating healthy, a sustainable diet must also take into account affordability, cultural relevance and whether it is really good for the environment, Lamarche emphasized.

Can a diet really save the planet?

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

“That’s huge,” Willett told CBC News from Cambridge, Massachusetts, “because it really means we can reforest some of our cultivated land… which would certainly help stabilize the global climate situation.”

Cattle graze in a field near Delegate, New South Wales, Australia, November 19, 2023 on a sunny day.
Cattle graze in a field near Delegate, New South Wales, Australia, in November 2023. (Peter Hobson/Reuters)

Climate change, caused largely by the burning of fossil fuels, is also exacerbated by agricultural emissions, including methane, a shorter-lived but more potent greenhouse gas. A negative feedback loop occurs when food production is threatened by drought and other extreme weather events, amplified and prolonged by climate change.

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

“If at a population level everyone reduced their intake of animal foods,” Bradbury said, “it would be much more efficient because we would be using that land to directly grow vegetable crops that we would eat.”

Willett says it is urgent to address the impact of our food on the climate.

“It’s scary and unique because it’s not linear, it’s accelerating. And we’re reaching tipping points that will be irreversible.”

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