A new study claims that eating lettuce could be .

The study, conducted by researchers at Carnegie Mellon University, compares the greenhouse gas emissions from the production of 1,000 calories of different foods.

On a per-calorie status, many of the “healthier” foods that the USDA promotes in their guidelines, like fruits, vegetables, dairy, and seafood, are resource-intensive per calorie.

Eating lettuce is three times more harmful to the environment than eating bacon.

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The example used earlier, lettuce, produces three times more greenhouse gas emissions than bacon.

Lettuce has so few calories that it would require someone to eat at least two whole iceberg lettuces to come close to the caloric intake equal to two slices of smoked back bacon. As a result, emissions from transporting lettuce are much higher per calorie than pork.

“There’s a ,” Michelle Tom, a Ph. D. student in civil and environmental engineering, told Carnegie Mellon News. “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.”

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If Americans were to switch their diet to adhere to the Agriculture Department’s 2010 dietary recommendations, it would result in a 38 percent increase in energy use, a 10 percent rise in water use, and a 6 percent jump in greenhouse gas emissions, the study finds.

But this isn’t to say that all vegetables are bad and negatively impacting the environment. Foods like onions, okra, carrots, broccoli, and Brussels sprouts all leave a less significant environmental mark. Lettuce, however, is more difficult to grow, harvest, and transport, and, in turn require significant amounts of water and energy to produce.

The study was set out to find if the obesity epidemic in America is negatively affecting the environment. Though it’s true that weight loss and consuming fewer calories reduces energy use, the USDA’s recommendations for healthy eating (more greens and less meats) , says the San Francisco Chronicle.

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