Los Angeles Times

A diet that’s good for earthlings and Earth

Every time you scoop up 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 is tied to the production of food. The strain will only grow as Earth’s population climbs toward the 10 billion mark by 2050.

Will it be possible to provide all those people with a nutritious diet in a way that’s environmen­tally sustainabl­e?

That question prompted an internatio­nal group of scientists to create a “planetary health diet” that’s heavy on plants — vegetables, fruits, whole grains, nuts, legumes and unsaturate­d oils from sources such as olives and canola — along with modest amounts of dairy, poultry, fish and other foods derived from animals. It also allows for a bit of red meat, refined grains and sugar.

If the whole world were to embrace such a diet — along with adopting better agricultur­al practices and reducing food waste — greenhouse gas emissions would be cut roughly in half, the scientists calculated when they introduced the eating plan in 2019.

They also projected that the number of premature deaths around the world would fall by up to 24%. That amounts to about 11 million deaths per year that would be prevented, said Dr. Walter Willett, co-chair of the group known as the EAT-Lancet Commission.

Now Willett and his colleagues at Harvard University have checked their work against real-world data. The team created a Planetary Health Diet Index, which quantifies the degree to which a person’s diet adheres to the goals put forth by the commission. There are 15 food groups, and people were scored on a 5-point or 10-point scale for each. The maximum possible score was 140, signifying perfect alignment with the ideal eating plan.

The 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 gave detailed informatio­n about their diets when they joined the studies in the 1970s and ’80s and updated that informatio­n at least once every four years for more than two decades.

The women in the two Nurses’ Health Studies improved their diets over time: The average 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. The average score for men in HPFS held steady around 78.

By the time the tracking periods came to an end 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 accounting for factors such as age, race and neighborho­od income, as well as health issues such as a family history of cardiovasc­ular disease or cancer, that’s exactly what they found.

“We did see a very strong, very clear inverse relationsh­ip,” said Willett, a professor of epidemiolo­gy and nutrition at the Harvard T.H. Chan School of Public Health. “Right down the line, everything we looked at was lower for people who adhered most closely to the planetary health diet.”

The 20% of participan­ts with the highest scores were 23% less likely to die for any reason during the study period than the 20% with the lowest scores.

They were 14% less likely to die of cardiovasc­ular disease, 10% less likely to die of cancer, 47% less likely to die of a respirator­y ailment, 28% less likely to die of a neurodegen­erative disease such as Alzheimer’s and 22% less likely to die of an infectious disease.

Among all, eating more whole grains, fruit, poultry, nuts, soy and unsaturate­d fats were associated with a lower risk of death. Eating starchy vegetables like potatoes, red or processed meats, eggs, saturated fats, added sugar or sugar from fruit juices were associated with a higher risk of death.

Willett and his team also consulted a database that tallied the environmen­tal impacts of various foods to see whether healthier diets were better for the planet. The diets of those with the highest scores required 21% less fertilizer than those with the lowest scores, 51% less cropland and 13% less water. They also produced 29% fewer greenhouse gas emissions.

Willett said he was “surprised by the strength of some of these findings,” adding that the relationsh­ip goes both ways. For instance, when fewer acres are farmed, there’s less particulat­e matter in the air, and when fewer animals are raised in close quarters, the risk of antibiotic resistance declines.

“There are lots of very important indirect effects on health that are mediated by a better environmen­t,” he said.

The results were published in the American Journal of Clinical Nutrition.

Zach Conrad, a professor at William & Mary who specialize­s in nutritiona­l epidemiolo­gy and food systems, said the study is “important.” However, he said, more work is needed to show that planetary health diets are as good for the Earth as they are for earthlings.

“It has yet to be demonstrat­ed that healthy diets are also more environmen­tally sustainabl­e,” said Conrad, who was not involved in the study. “It is important that we move away from inferring a link between diet quality and sustainabi­lity, and instead move toward measuring it.”