If you read the press release for a new study coming out of Carnegie Mellon ("Vegetarian and 'Healthy' Diets Could Be More Harmful to the Environment"), you may be forgiven for getting a bit smug as you order that side of bacon. Unfortunately, it's way oversold. The study, published in the journal Environment Systems and Decisions, wasn't actually set up to answer this, and it did not even look at vegetarian — let alone vegan — diets.
The researchers' actual intention was to look at how obesity is affecting the environment in the U.S., which they did by comparing three dietary scenarios in terms of their greenhouse gas emissions, use of resources, and blue water footprint (the volume of surface and groundwater). In the first scenario, they reduced calories, but made no changes to the type of food people were eating. The second did not reduce calories but looked at people whose diets reflected the 2010 USDA Dietary Guidelines (i.e., eating lots of fruits and vegetables and lean meats and fish). The third scenario reduced calories enough so people would weigh normal weights (rather than being obese) and adhered to USDA guidelines.
What they found, to the surprise of lead author Michelle Tom, was that scenario two turned out to be the worst for the environment. "Initially, I expected all of the impacts to decrease when shifting from our current diet to the USDA recommended diet," says Michelle Tom, a Ph.D. student at Carnegie Mellon University and lead author of the study. "But in fact, impacts (energy use, water use, and emissions) increased, which was the complete opposite of what I expected."
More specifically, shifting to dietary scenario one — simply reducing calories — decreases energy use, blue water footprint, and greenhouse gas emissions by around 9 percent, while shifting to dietary scenario two increases energy use by 43 percent, blue water footprint by 16 percent, and GHG emissions by 11 percent. Shifting to dietary scenario three increases energy use by 38 percent, blue water footprint by 10 percent, and GHG emissions by 6 percent.
"The data makes quite a bit of sense," says Ronald Amundson, a UC Berkeley professor of environmental science policy and management who was not involved with the study. "Fruit and vegetables have (generally) low calories, and the analysis, rightfully so, is based on resources per calorie of food energy. Fruits and vegetables, on average, require more irrigation and have lower GHG emissions relative to many of the other food groups."
But doesn't red meat production create huge amounts of greenhouse gas emissions? Yes. The researchers acknowledged this in their paper, and it has been noted many times, that meat products have the highest emissions. But certain vegetables, such as lettuce and eggplant, do require significant amounts of energy and water.
"This study's results demonstrate how the environmental benefits of reduced-meat consumption may be offset by increased consumption of other relatively high-impact foods, thereby challenging the notion that reducing meat consumption automatically reduces the environmental footprints of one's diet," Tom says.
The veggie- and fruit-heavy diet had the worst impact on the environment not only because it required subjects to shift their consumption patterns toward higher-impact foods such as seafood, Tom says, "but we're also not reducing our caloric intake. Dairy has the greatest impact on increased emissions when shifting to the USDA diet because not only does dairy have high emissions per calorie, but under the USDA dietary guidelines, we are supposed to significantly increase our consumption of dairy products."
The Omnivore's Dilemma
A vegan diet has been shown to have a smaller environmental impact than just about any other, but there are gray areas once you veer into more omnivorous territory. Add dairy to your diet, and you need to account for the fact that the average cow belches out 117 pounds of methane a year, which is 25 more times more damaging than carbon dioxide, according to a 2013 report by the Food and Agriculture Organization of the United Nations.
In addition to methane, meat production produces nitrous oxide, which is 300 times as potent as CO2, and the resultant manure pollutes water and the air, and almost 20 percent of edible meats wind up in landfills.
Something else to consider: A story in the Washington Post pointed out that the paleo diet, rich in meat and vegetables but fewer carbs, is the worst in terms of environmental impact. "As our results show, food consumption behaviors are more complex," Tom says, "and the outcomes more nuanced."
So what does an environmentally sound, nuanced diet look like? The best answer isn't as simple as eschewing vegetables in favor of bacon. Because red meat consumption is expected to rise significantly by 2050, reversing the trend would have a tremendous impact on greenhouse gas emissions, a 2014 study published in Nature concluded. It's going to take global government intervention to make the impact desperately needed. Significant improvements to production methods could positively impact the environment more than simply eating less meat, and better quality feed, for another example, would reduce nitrous oxide emitted by its production.
This study "does point out that serious accounting is needed before we assume certain actions have an impact," Amundson says. As important as agriculture and consumption are to enviro conservation, however, our biggest problem is reducing our reliance on fossil fuel, many climate scientists say. But as columnist and oyster farmer Tamar Haspel points out, "One decision trumps every other — potentially by orders of magnitude — and that's how many children you have. No amount of bean-eating or Prius-driving will compensate for reproducing, and it's the childless, not the vegetarians, who are more likely to save the planet."
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