This Diet May Protect Your Health, and the Planet

Can food that's healthy for humans also be what's best for the planet? According to a new study, a sustainable diet was associated with a lower risk of premature death.

The research, led by the Harvard T.H. Chan School of Public Health and published in the American Journal of Clinical Nutrition in June, tested the Planetary Health Diet, which was developed by a commission of researchers gathered by The Lancet in 2019, who study fields like nutrition, health and the environment.

The diet, which is designed to be both healthy and sustainable, emphasizes eating plant-based foods like fruit and vegetables; getting protein from plants such as legumes, consuming a limited amount of animal-based products; and minimizing saturated fat, refined grains and sugar.

After scoring how closely participants kept to the Planetary Health Diet over about 30 years, the researchers found that compared to people who scored the lowest, the top quintile were 23% less likely to die of any cause. They were also less likely to die of the major causes of disease: cardiovascular (by 14%), cancer (by 10%), respiratory (by 47%), and by neurodegenerative (by 28%). Their diet also produced environmental benefits, including 29% lower greenhouse gas emissions and 51% lower land use.

"The bottom line is there were huge benefits for health and the environment," said Walter Willett, a co-author, a member of the commission that devised the Planetary Health Diet and a professor of epidemiology and nutrition at Harvard T.H. Chan School of Public Health.

Diets are notoriously difficult to study, because there are so many factors scientists can't control, given there's such variability between people's bodies, meals and everyday routines. Many nutrition studies, including this one, are observational: scientists try to record what's happening out in the world. In this case, that means that the participants tried to remember what they'd eaten (instead of, for instance, the scientists feeding the participants every meal).

Even with these limitations, this observational study was particularly thorough. Its participants, over 200,000 medical professionals in three studies, responded to surveys about their diets every four years. The researchers tracked whether the participants died and from what causes over the course of the study.

Lawrence Kushi, a researcher who studies nutrition epidemiology at the Kaiser Permanente Northern California Division of Research and did not work on the study, underscored that the study isn't a perfect measurement of either what people ate or its environmental impact — for instance, the diet didn't look closely at nutritional adequacy.

You might miss nutrients if you don't have enough varieties of foods within each group. However, he said the study shows both that "the food choices that you make, make a big difference in terms of your overall health," and that healthy eating can be "surprisingly aligned" with sustainability.

Credit: EAT Foundation

Ty Beal, a global nutrition and food system scientist at the Global Alliance for Improved Nutrition, who did not work on the study, said that he thinks the Eat-Lancet commission overstated that unprocessed red meat is harmful for health, and noted that his own research found that there were certain gaps in the Planetary Health Diet. (Willett disagreed that the diet doesn't provide sufficient zinc and iron and argued that the major driver of Vitamin D deficiency is a lack of sun. He said that Zinc deficiency isn't a serious challenge in the U.S., and that vitamin deficiencies can be addressed by taking multivitamins).

However, Beal pointed out that there are useful lessons to take away from the diet, especially the importance of eating minimally processed, plant-based foods, and increasing plant-based proteins like beans and lentils.

"The diet seems really healthy overall, much better than the status quo," said Beal. "Because right now, diets are really poor. And there are a lot of great things on the sustainability side."

One takeaway from the research is that improving your diet offers benefits at any age, says Willett. At virtually any life stage, he said, people who started eating closer to the Planetary Health Diet had a reduction in mortality. Even if you don't have a good diet or lifestyle, he said, "if you made it to 50 and you want to improve your chances of longer health and lower mortality, it's not too late."

Kushi also pointed out that people whose eating didn't follow the diet perfectly benefited more than people with the lowest scores. "Doing a lot is always better, but doing a little is also beneficial," he said. "The takeaway isn't necessarily that you have to become a vegan, you have to cut out all red meat. It's: every little bit makes a difference."

The Planetary Health Diet is also a reminder that what we eat has a major impact on the planet. Researchers have estimated that if everyone on the planet followed the dietary pattern along with cutting food waste and improving agricultural practices, greenhouse gas emissions could be cut in half by 2050.

If your goal is to reduce your environmental impact, Willett suggests cutting back on animal products, and choosing options with less environmental impact when you do: for instance, grass-fed meat, small fish like anchovies, sardines, or bivalves like mussels.

It may also be worthwhile to try to learn more about where your food comes from, says Kushi, and to choose food that's in season or was produced close by, although he acknowledges that not everyone has access to this information.

Ultimately, making diets healthier and more sustainable can't be up to individual choices alone. Not everyone has access to healthy food, many researchers argue that improving food sustainability will require major global change in food systems.

However, whether you feel most motivated to change your diet to help the planet or to improve your personal health, "Your personal food choices can make a difference," says Kushi.

Tara Lawis a freelance journalist writing about health and equity. A graduate of Columbia Journalism School, she most recently worked as a staff reporter for TIME Magazine. Read More