A new study finds that the more people followed environmentally sustainable diets that emphasized plant nutrients, the lower the risk of death from cancer, heart disease, Alzheimer's disease and a variety of other causes.
(JM Hirsch/Associated Press)
Every time you reach for a spoonful of overnight oats or sink your teeth into a cheeseburger, you're eating for two, for the sake of your own health and the health of the planet.
Researchers estimate that about 30% of greenhouse gas emissions, 40% of land use, and 70% of freshwater use are linked to food production. The tension will only grow as Earth's population reaches the 10 billion mark by 2050.
Will it be possible to provide all these people with a nutritious diet in an environmentally sustainable way?
That question led an international group of scientists to create a “planet-healthy diet” rich in plants, including vegetables, fruits, whole grains, nuts, legumes, and unsaturated oils from sources like olives and canola, along with modest amounts of dairy. . poultry, fish and other foods derived from animals. Also allow some red meat, refined grains and sugar. (You can even eat a hamburger once a week.)
If everyone adopted a diet like this, along with adopting better farming practices and reducing food waste, greenhouse gas emissions would be cut by about half, scientists calculated when they introduced their eating plan in 2019. Also They projected that the number of premature deaths worldwide would be reduced by up to 24%.
“That equates to about 11 million deaths a year,” something that wouldn't happen, said Dr. Walter Willett, co-chair of the group known as the EAT-Lancet Commission.
Now Willett and his colleagues at Harvard University have compared their work with real-world data.
The Harvard team created a Planetary Health Diet Index, which quantifies the degree to which a person's diet adheres to the goals set by the commission. There are 15 food groups and people were rated on a 5 or 10 point scale for each. The maximum possible score was 140, which would mean perfect alignment with the ideal eating plan.
Researchers assigned PDHI scores to more than 200,000 people enrolled in the Nurses' Health Study, the Nurses' Health Study II, and the Health Professionals Follow-up Study. All participants gave detailed information about their diets when they joined the studies in the 1970s and 1980s, and they updated that information at least once every four years for more than two decades.
Women in the two Nurses' Health Studies improved their diet over time: the average index score for participants in NHS1 increased from 75.7 in 1986 to 84.5 in 2010, while the average for women in NHS2 jumped from 70.4 in 1990 to 85.9 in 2015. However, men's mean HPFS score remained stable at around 78.
When the follow-up periods ended in 2019, 54,536 people in the three studies had died.
The researchers hypothesized that the higher a person's PDHI score, the lower their risk of being among the deceased. And after taking into account demographic factors like age, race, and neighborhood income, as well as health issues like a family history of cardiovascular disease or cancer, that's exactly what they found.
“We saw a very strong and very clear inverse relationship,” said Willett, a professor of epidemiology and nutrition at the Harvard TH Chan School of Public Health. “Going forward, everything we observed was lower for people who followed the planetary health diet more closely.”
Compared to the 20% of people with the lowest scores, the 20% with the highest scores were 23% less likely to die from any reason during the study period. They were also 14% less likely to die from cardiovascular disease, 10% less likely to die from cancer, 47% less likely to die from respiratory disease, 28% less likely to die from neurodegenerative disease such as Alzheimer's and 22% less likely to die from cardiovascular disease. less likely to die from an infectious disease.
Among all men and women, eating more whole grains, fruits, poultry, nuts, soy and unsaturated fats was associated with a lower risk of death. On the other hand, eating more starchy vegetables such as potatoes, red or processed meats, eggs, saturated fats, added sugar or sugar from fruit juices was associated with a higher risk of death.
Willett and his collaborators also consulted a database that tallied the environmental impacts of various foods to see if healthier diets were better for the planet. Compared to the diets of people with the lowest PDHI scores, the diets of those with the highest scores required 21% less fertilizer, 51% less cropland and 13% less water and produced a 29% less greenhouse gas emissions.
Willett said he was “surprised by the strength of some of these findings,” adding that the relationship cuts both ways. For example, when fewer acres are farmed, there are fewer particles in the air, and when fewer animals are raised in close quarters, the risk of antibiotic resistance decreases.
“There are many very important indirect effects on health that are mediated by a better environment,” he said.
The results were published Monday in the American Journal of Clinical Nutrition.
This is not the first study to link planet-healthy diets with a reduced risk of premature death; Researchers have seen the connection in the United Kingdom and Sweden. But the new work is the first to apply a more precise dietary index to a large sample of Americans and use it to assess their risk of death.
This is an “important” advance, said Zach Conrad, a professor at William & Mary who specializes in nutritional epidemiology and food systems.
However, he said more work is needed to prove that planet-healthy diets are as good for Earth as they are for Earthlings.
“It has not yet been proven that healthy diets are also more environmentally sustainable,” said Conrad, who was not involved in the new study. “It is important that we stop inferring a link between diet quality and sustainability and instead move towards measuring it.”
