There is a scene in the 2013 film Escape Plan in which Arnold Schwarzenegger and Sylvester Stallone face off in the canteen of a maximum security prison. Arnie throws the first punch, flooring Stallone in front of the baying crowd of fellow prisoners.Stallone, when he gets to his feet, responds with a left hook fierce enough to knock out most puny mortals. But it prompts only a chuckle from the old slugger who played the Terminator."You punch like a vegetarian," he says, in that unmistakeable Austrian drawl.Yesterday, Arnie was back opining on the subject of eating meat. On this occasion, speaking at the UN Climate Conference, in Paris, the views of the 68-year-old bodybuilder turned actor turned politician were rather more cerebral- and surprising.During an interview following a speech to the conference, Schwarzenegger, the former governor of California, claimed 28% of all greenhouse gases are caused by intensive farming.As a result, he said, it was a "good idea" for people to stop eating meat altogether and at the very least stop for one or two days a week."Luckily, we know you can get protein in many different ways," he said.Schwarzenegger's comments were made at a time when an increasing number of experts are clamouring for us to turn vegetarian or, better yet, leave that butter dish in the fridge and go all out vegan.There is growing evidence of the strain our meat consumption is placing on the environment, with every 1kg of meat protein requiring the same amount of energy to produce as between 3kg and 10kg of vegetable protein.Last year, the UN Food and Agriculture Organisation released a report in which it was claimed that emissions from farming, forestry and fisheries had nearly doubled over the past half-century and might increase by another 30% by 2050.Most of those emissions emanate from nitrogen fertilisers and flatulent cattle, but the effects are exacerbated by the swathes of forests cut down to accommodate the animals.The call to go meat-free stems not just from concerns about climate change. A new government review on antibiotic resistance, published yesterday, warns that a prevalence of superbugs in undercooked meats is now putting lives at risk. The review found that the use of antibiotics in agriculture represents a "critical threat to public health". It warned of the increasing prevalence of drug-resistant strains in farmed animals that could be passed to humans.The persistence - and severity - of such warnings does seem to be making a difference. According to The Vegan Society, the number of vegans in the UK has doubled in the past nine years to around 300000.Bolstering their ranks is Barny du Plessis, a 41-year-old bodybuilder from Norwich who last year won the Mr Universe title.He turned vegan 10 months ago with his fiancee, Josie, who is also a body builder, partly for the environment and partly because meat-eating aggravated his hernias."All those problems disappeared," he says. "I was suddenly making leaner, better gains and my alkaline balance is really good. I never feel tired."Health journalist Anna Magee, the editor of healthista.com, earlier this year decided to embark on a 60-day trial of veganism and measure the effect on her health.The 46-year-old said she lost 6kg, gained muscle but lost cholesterol. She remains a vegan.But some medical experts are not convinced of the health benefits of giving up meat entirely. Professor David Haslam, a former GP and president of the British Medical Association, insists he will never turn vegetarian.He said: "Meat is part of a normal mixed and balanced diet. There are certain things you can get only from animal products. Humans have been eating it for tens of thousands of years. It can't suddenly be bad for us."Laura Piddock, professor of microbiology at the University of Birmingham and director of Antibiotic Action, said: "We are omnivores ... meat is a part of our diet. We farm animals to eat them and need to start realising that if we are going to eat these animals we need to look after them." ..