What you have for breakfast could have twice the impact on the environment as driving to work, according to a study published in New Scientist magazine.
Ecotrust ecological economist Astrid Scholz, who calculates food production carbon emissions using "equivalence CO2 emissions", says a bowl of cereal with milk has emitted as much greenhouse gas to get to your table as a 6km drive in an SUV would produce.
New Scientist said academics tallying the carbon emissions of products and manufacturing processes found our diets account for up to twice the emissions caused by driving.
Scientists say going vegetarian is a sure-fire way to reduce your carbon footprint, as livestock account for 18 per cent of "man-made" greenhouse emissions.
The report said the average American could lower his or her emissions by between 252kg and 400kg, simply by having one red-meat-free day a week.
And fish lovers should opt for plant-eating farmed fish like tilapia, carp, bream and catfish, which have a lower carbon footprint than wild and other farmed species.
Professor Caroline Saunders, director of Lincoln University's agribusiness and economics research unit, said eating meat left a higher carbon footprint "but you have to look at the broader issues of not eating meat. Like what would you do with the land?"
Professor Saunders said a switch to vegetarianism could cause new problems, similar to those arising out of the demand for biofuel crops.
"Comparing a vegan diet with a vegetarian diet, there is very little difference in emission reduction from cutting out eggs and dairy. Many people are not getting adequate nutrition as it is. You have to be cautious about recommending people cut down on red meat."
Professor Saunders co-authored the 2007 "Food Miles" Report.
The report compares the emission efficiency of New Zealand's dairy industry in producing and delivering products for the British market with the carbon footprint of meat and dairy produced in the UK for its local market.
The study's central findings showed the UK produced 35 per cent more emissions per kilogram of milk solids than New Zealand and 31 per cent more emissions per hectare.
WHAT IS CO2EQ?
* Food emissions are measured as "equivalence CO2 emissions" (CO2eq) and take account of every step of food production "from farm to fork".
* CO2eq is a more accurate way of saying "carbon footprint" as it includes carbon dioxide as well as other greenhouse gases such as methane and nitrous oxide.
* A bowl of cereal with milk has the CO2eq of a 6 km drive in an SUV.