Eating lettuce is apparently three times worse for causing greenhouse gas emissions than eating bacon.
USDA recommendations to consume more fruits, vegetables, dairy and seafood were more harmful to the environment, new research from Carnegie Mellon University in the United States found.
Those foods had relatively high resource uses and greenhouse gas emissions per calorie, Paul Fischbeck, one of the study's authors, said.
Lots of common vegetables required more resources per calorie to produce than you would think, Professor Fischbeck said.
Eggplant, celery and cucumbers looked particularly bad when compared to pork or chicken, he said.
There was a complex relationship between diet and the environment, and Professor Fischbeck said what was good for humans health-wise wasn't always what's best for the environment.