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“Dietary change could have large health and environmental benefits,” says Marco Springmann, the lead author of the new study in the Proceedings of the National Academy of Sciences, and a sustainability researcher at Oxford University (all four researchers involved in the work were from Oxford). But the study itself acknowledges that the research in some ways represents an idealized experiment, and changing food systems as dramatically as envisioned in the study would be a momentous task.

The researchers say it is “the first time, to our knowledge,” that health models and emissions models have been joined together in this way.

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Much recent research has highlighted how agriculture, and especially eating meat, contributes to climate change. Ruminant animals, like cattle, belch methane into the air as part of their process of digestion. Methane is a potent greenhouse gas, especially over short time frames of several decades — which is when the key decisions about mankind’s steps to address climate change will be made.

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In addition, if tropical zones are deforested to make way for ranching, then animal agriculture can drive climate change in another way, since the planet’s forests are major storage areas for carbon that might otherwise end up in the atmosphere.

Meanwhile, the World Health Organization has recently charged that eating processed meats can be a risk factor for cancer, and a large body of health research points to the importance of consuming adequate fruits and vegetables in your diet to stave off a number of deleterious health outcomes.

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Taking all of this as a premise, the new study uses a computerized model to examine four different dietary scenarios, for regions of the world and the planet as a whole, out to the year 2050. One is a standard “business as usual” outlook for our global diet, based on projections by the Food and Agriculture Organization of the U.N.

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The second study scenario, by contrast, assumed a nation-by-nation implementation of a healthier diet in which people, on average, get adequate calories based on eating required amounts of fruits and vegetables, and consuming less meat and sugar (and not over-eating). That diet, says Springmann, consists of a “minimum 5 portions of fruit and veg, and half a portion of red meat per day.” It was based on expert assessments of a healthier diet and required energy intake by the World Health Organization and Food and Agriculture Organization.

In another scenario, the study also considered an even stronger dietary shift toward vegetarianism; and, finally, a shift of diets toward full veganism. In both of those diets, the food eaten was consistent with dietary guidance from the World Health Organization.

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The research notes that these diets, as modeled in the study, are “not intended to be realizable dietary outcomes on a global level but are designed to explore the range of possible environmental and health outcomes of progressively excluding more animal-sourced foods from human diets.” It acknowledges that “large changes in the food system would be necessary to achieve” them and that, in truth, it is not expected that the world’s human population will get enough fruits and vegetables, or even food as a whole, over the first half of this century. (795 million people don’t get enough food in the world at present, according to the U.N. World Food Programme.)

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Just to underscore this point, the healthy-eating diet alone would require 25 percent more fruits and vegetables consumed globally, and 56 percent less meat. The vegetarian and vegan diets require even larger shifts.

Springmann acknowledges that the changes that would be required — not just political or industrial, but cultural — would be massive. “We first want to show, is it actually worth thinking about it,” says Springmann. “And we show, yeah, it’s definitely worth thinking about it, and we hope with those numbers, we encourage more research and action to see how we get there.”

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Certainly, the changes are striking — the healthy diet led to 5.1 million fewer global deaths per year in the model by 2050, from conditions like heart diseases, stroke, and cancer, especially in developing countries. The researchers said that more than half of the effect was from reductions in meat consumption (other factors included less over-eating). The other diets, in the model, saved even more lives.

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At the same time, implementing these diets greatly cut greenhouse gas emissions from the food and agriculture sector. With the healthy diet that still contained some meat, global greenhouse gas emissions from the food sector only increased 7 percent by 2050, compared with an expectation of a 51 percent increase under business as usual. Again, the vegetarian and vegan diets had even sharper effects on emissions.

And as the study notes, “we did not account for the beneficial impacts of dietary change on land use through avoided deforestation,” meaning that the theoretical reductions in greenhouse gases could be even higher.

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“We disagree with the premise of the study,” said Janet Riley, senior vice president for public affairs at the North American Meat Institute, by email, noting that the institute had not yet had the opportunity to review the research in detail.

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“The authors suggest that somehow consensus exists that a diet that is lower in meat is healthier and we would argue that no such consensus exists. In fact, recent research is actually pointing to the health benefits of a balanced diet that includes meat in ensuring brain development in children, maintaining brain function later in live, preventing sarcopenia and anemia and so on,” Riley said.

Frank Mitloehner, a professor in the department of animal science at the University of California at Davis, pointed out that in the U.S., livestock related emissions only amount to 4.2 percent of the overall total. “Comparing the 4.2% GHG contribution from livestock to the 27% from the transportation sector, or the 31% from the energy sector in the United States, puts all contributors into perspective,” Mitloehner wrote in a document sent in response to a query about the new study.

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But Mitloehner added that in other countries, the percentage of total emissions coming from livestock can be much higher.

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Overall, the ability to cut emissions from the food sector could still be significant, because of the urgent quest, embraced by the nations of the world, to ramp down greenhouse gases quickly in the next few decades to avoid warming more than 2 degrees Celsius above pre-industrial temperatures.

And as if that’s not enough, the research finds that these dietary shifts could reduce healthcare costs — in the U.S. more than any other nation, in fact.

“In terms of healthcare benefits, because the health expenditure is so large in the U.S., we find that the pure healthcare savings that would be associated with dietary shifts would be the largest actually of all countries,” says Springmann. By contrast, two-thirds of the actual health benefits of the dietary shifts would occur in developing nations, the research found.

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Granted, any major shift of global diets would implicate huge changes in government policy and in industry — and might trigger some major resistance, not only from food producers, but also from individuals who, to put it bluntly, like to eat meat.