New research has shown that on a per-calorie basis, the carbon emissions from the production of fruit and vegetables can be much higher than for meat.

It means that, contrary to recent headlines and comments by actor Arnold Schwarzenegger, eating a vegetarian diet could in fact contribute to climate change.

According to a study from Carnegie Mellon University in the US, consuming more fruits, vegetables, dairy and seafood is more harmful to the environment because those foods have relatively high resource uses and greenhouse gas (GHG) emissions per calorie.

The study measured the changes in energy use, blue water footprint and GHG emissions associated with food consumption patterns.

“Eating lettuce is over three times worse in greenhouse gas emissions than eating bacon,” said Paul Fischbeck, professor of social and decisions sciences and engineering and public policy.

“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.”

The research team studied the food supply chain to determine how high levels of consumption are affecting the environment.

Specifically, they examined how growing, processing and transporting food, food sales and service, and household storage and use take a toll on resources in the form of energy use, water use and GHG emissions.

On one hand, the results showed that eating fewer calories has a positive effect on the environment and reduces energy use, water use and GHG emissions from the food supply chain by approximately 9 percent.

However, eating the recommended “healthier” foods - a mix of fruits, vegetables, dairy and seafood - increased the environmental impact in all three categories: Energy use went up by 38 per cent, water use by 10 per cent and GHG emissions by 6 per cent.

“There's a complex relationship between diet and the environment,” researcher Michelle Tom said.

“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 cognisant of these tradeoffs as they develop or continue to develop dietary guidelines in the future.”

The complete study is accessible here.