Vegetarians could be destroying the environment, ironically worse than their meat-eater counterparts. Researchers at Carnegie Mellon took a closer look at foods recommended by the U.S. Department of Agriculture (USDA) and discovered fruits, vegetables, dairy, and seafood is more harmful to the environment than red meat. Their study, published in the journal Environment Systems and Decisions, explains how healthy foods require greater amounts of resources and greenhouse gas (GHG) emissions per calorie.

"Eating lettuce is over three times worse in greenhouse gas emissions than eating bacon," said the study’s co-author Paul Fischbeck, professor of social and decisions sciences and engineering and public policy, in a press release. "Lots of common vegetables require more resources per calorie than you would think. Eggplant, celery, and cucumbers look particularly bad when compared to pork or chicken."

Fischbeck and his colleagues studied the food supply chain in order to trace it back to how the obesity epidemic impacts the environment. They looked at everything from the growing, processing, transporting food, food sales, service, household storage, energy use, water use, and GHG emissions.

It turns out, when a person gets their weight under control they eat fewer calories, which has a positive effect on the environment and reduces energy use, water use, and GHG emissions by 9 percent. But when they replace unhealthy foods with healthier mix of fruits, vegetables, dairy, and seafood it negatively impacted the environment. Energy use went up by 38 percent, water use by 10 percent, and GHG emissions by 6 percent.

"There's a complex relationship between diet and the environment," said the study’s co-author Michelle Tom, a PhD candidate in civil and environmental engineer, in a press release. "What is good for us health-wise isn't always what's best for the environment. That's important for public officials to know and for them to be cognizant of these tradeoffs as they develop or continue to develop dietary guidelines in the future."

On the flip side, researchers recently teamed up with their local food bank and crunched the numbers and found that a healthier vegetarian diet can save the average American roughly $750 each year compared to meat-laden diets. Aside from vegetarian diets being healthier and most cost-efficient, the one blatant downside is the negative environmental impact, and that could change with innovations in building better agricultural systems.

Source: Hendrickson CT, Fischbeck PS, and Tom MS. Energy use, blue water footprint, and greenhouse gas emissions for current food consumption patterns and dietary recommendations in the US. Environment Systems and Decisions. 2015.