Halving the amount of meat and dairy eaten in Europe could slash nitrogen pollution from agriculture, improve health and boost food exports, a study has suggested.
Around four-fifths of nitrogen emissions in the European Union come from agriculture , for example from fertiliser and manure, and between 79% and 88% of the sector's nitrogen losses into the environment are linked to livestock production.
Nitrogen emissions in the form of ammonia, nitrates and nitrous oxide can cause air, water and soil pollution and account for around 10% of the warming caused by greenhouse gases, experts said.
If everyone in the EU became "demitarian" - halving the amount of meat and other animal products they consume - it could reduce greenhouse gases from agriculture by 25% to 40% and nitrogen emissions by 40%, the European Nitrogen Assessment's "nitrogen on the table" report said.
It would also bring European consumption of saturated fats down to within levels recommended by the World Health Organisation and reduce red meat and protein consumption, cutting the risk of heart disease and cancer.
Because around 80% of crops are fed to livestock, reducing meat and dairy consumption would free up land for other crops or for plants grown to produce bio-energy.
It would also slash soya bean imports to the EU by around three-quarters.
But with livestock production responsible for 60% of the output of EU agriculture, a radical change in diets could have a major economic impact, although there could be a boost in revenue from increased cereal production and export.
The study, which did not include sheep and goat products, found there were large differences between the nitrogen "footprint" of different types of food, with 25 times as much nitrogen being lost to the environment per unit of food protein from beef than cereals.
Pigs, poultry, eggs and dairy are responsible for around 3.5 to eight times the amount of nitrogen losses from cereals.
The report's lead author Henk Westhoek, from the Netherlands Environmental Assessment Agency, said: "The report shows that the nitrogen footprint of meat and dairy is considerably higher than that from plant-based products.
"If all people within the EU would halve their meat and dairy consumption, this would reduce greenhouse gas emissions from agriculture by 25% to 40% and nitrogen emissions by 40%.
"The EU could become a major exporter of food products, instead of a major importer of, for example, soya beans."
The report's co-author Professor Mark Sutton, from the UK's Centre for Ecology and Hydrology, said: "There are many ways in which society could improve the way it uses nitrogen, and this includes actions by farmers and by ourselves.
"Our new study shows that adopting a demitarian diet across Europe would reduce nitrogen pollution levels by about 40% which is similar to what could be achieved by adopting low-emission farming practices."
Prof Sutton acknowledged that other countries were increasing their intake of meat and dairy as they sought more western diets and patterns of consumption, with the UK Government urging farmers to make the most of export opportunities.
But he suggested that if Europeans made the shift to a less meat and dairy-heavy diet, it would have a cultural impact in changing the trajectory of increases in other countries.
He also said that urging people to become vegetarian could cause a backlash, because people wanted to eat meat, but experts studying the issue of nitrogen pollution had demonstrated how it was possible to become "demitarian" by halving the amount of meat served at their conferences.
"From the environmental point of view, it's not about whether you eat meat and dairy or not, it's about how much," he added.