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Why the best diet for you is also good for the planet

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Can you eat a diet that's good for your health and good for the planet?

A new study suggests that it's possible. It found that people who ate mostly minimally processed plant foods such as nuts, beans, fruits, vegetables, whole grains and olive oil, along with modest amounts of meat, fish, eggs and dairy, had lower rates of premature death from heart disease, cancer and other chronic diseases.

At the same time, their diets had a smaller environmental footprint because they consisted of foods that were grown using relatively less land and water and that were produced with fewer greenhouse gas emissions.

The study, published Monday in the American Journal of Clinical Nutrition, was inspired by a landmark 2019 report from the EAT-Lancet Commission, which designed a "Planetary Health Diet" capable of sustaining 10 billion people and the planet by 2050. The planetary health diet, in broad strokes, encourages people to eat more plants and whole foods alongside small portions of meat and dairy. It was designed to be flexible and adaptable to different cultural, culinary, and personal preferences.

The new report is among the first large studies to examine how eating within the contours of the planetary health diet affects a person's likelihood of dying prematurely from major diseases. The study analyzed data on more than 200,000 men and women in the United States who were followed closely for over three decades. The new study found the following:

How to follow a planetary diet

In the study, people whose eating habits adhered closely to the planetary health diet ate large amounts of the following foods:

Walter Willett, a senior author of the new study and a professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, stressed that adopting a planetary health diet does not require giving up meat.

He described it as an omnivorous diet that makes room for two servings a day of animal foods. A typical week on the diet, for example, might include one daily serving of dairy such as milk, cheese, or yogurt, a weekly serving of red meat, one weekly serving of eggs, two weekly servings of poultry, and two weekly servings of fish.

The diet prioritizes generous amounts of fruits, nuts and vegetables and a variety of plant sources of protein such as beans, lentils and other legumes, which makes it relatively easy to follow, Willett said.

"You can put these pieces together with the flavors and foods of almost every traditional culture," he added. "There's a lot of flexibility."

How healthy eating slows climate change

Food production accounts for about 30 percent of all greenhouse gas emissions worldwide. Much of that is driven by methane emissions from livestock, widespread deforestation, and emissions from food processing, farm machinery, the use of synthetic fertilizers and other aspects of agricultural production.

Most of the cropland in America is used to grow just two crops — corn and soy — that are fed to livestock. This practice of monoculture farming can degrade soil, reduce biodiversity and require more irrigation, pesticides and herbicides. Only about 5 percent of farmland in America is used to grow other vegetables, fruits, nuts and legumes, Willett said.

Changing our diets and our food production system will not be enough on their own to put the brakes on climate change, but they are important steps, Willett said.

"What this study shows is that we can both shift our diets to be far healthier than the average American diet and also at the same time have a substantial impact on slowing down climate change," he added. "We don't have to trade off planetary health for human health. We can have both — it's a double win."

The new study was observational, meaning it found correlations between what people ate and their risk of major diseases, not necessarily cause and effect. It's possible that other lifestyle behaviors could explain the findings. But the researchers took into account factors such as whether the participants smoked, exercised, drank alcohol, or had family histories of heart disease, cancer and other diseases. The health benefits of eating a diet high in nuts, olive oil, whole grains, fruits and vegetables have also been documented in rigorous clinical trials.

Marion Nestle, an emeritus professor of nutrition, food studies and public health at NYU, said the federal government should adopt food policies to promote diets that are not only nutritious but sustainable. "The government could produce clear dietary guidelines, set healthier standards for school meals, support production of food for people — rather than feed for animals or fuel for cars — and stop subsidizing industrial production of meat," said Nestle, who was not involved in the new study.

Do you have a question about healthy eating? Email EatingLab@washpost.com, and we may answer your question in a future column.

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