Scientists have measured how much different lunch sandwiches hurt the environment. CC0 Creative Commons

Even something as basic as eating a sandwich for lunch can be bad for the environment.

Researchers estimated the carbon footprint of 40 different kinds of sandwiches based on their ingredients and packaging. According to their study in the journal Sustainable Production and Consumption, homemade sandwiches have half the impact of ready-made sandwiches, so it is better for the environment to make your own lunch. The most environmentally friendly homemade sandwich was a simple ham and cheese.

That’s despite the fact that sandwiches with pork and cheese overall had a higher carbon footprint than others.

The carbon impact comes from the “agricultural production and processing of their ingredients,” the University of Manchester noted. Elements like packaging, refrigeration and transporting the materials also play into it.

On the lowest end of the sandwich scale, the impact of a homemade ham-and-cheese, constructed with a particular recipe, was measured to be the equivalent of the amount of carbon dioxide a car would add to the atmosphere while driving a little more than 3 miles. A ready-made bacon, egg and sausage sandwich, which carried the greatest impact of the sandwiches tested, was found to be the equivalent of driving for 12 miles.

“Sandwiches are ubiquitous food items and yet little is known about their environmental impacts,” according to the study.

Through reducing food waste, changing packaging and other tweaks, it’s possible the reduce the impact of ready-made sandwiches substantially, the authors wrote.

“We need to change the labelling of food to increase the use-by date, as these are usually quite conservative,” researcher Adisa Azapagic said in the university statement. “Commercial sandwiches undergo rigorous shelf-life testing and are normally safe for consumption beyond the use-by date stated on the label.”

Cutting out the environmentally costly meat, cheese, lettuce and tomato from a sandwich’s ingredients will also decrease the carbon footprint.