Our diets are ruining our health, and the planet. So what can we do to help?.

As part of the research for his latest film, Okja, the Korean director Mr Bong Joon-ho visited an abattoir in Colorado. The experience of witnessing animal slaughter on an industrial scale affected not only his movie, but also his eating habits. Mr Bong became vegan for two months. Although he was later lured back to meat by the mouthwatering promise of Korean barbecue, he has said he is now steadily transitioning to a permanent pescatarian diet.

Mr Bong’s movie has had a similar effect on audiences. It tells the story of a Korean girl’s quest to save her pet, Okja, a genetically enhanced super-pig, from the slaughterhouse. Many viewers say it turned them vegetarian, at least temporarily. Co-written by Mr Jon Ronson (a pescatarian), Okja has villains who embody the horrors of the meat industry: the sociopathic CEO of a food multinational, played by Ms Tilda Swinton, and the company’s unhinged vet, played by Mr Jake Gyllenhaal.

For some, the film appears to have been a more emotionally affecting indictment of industrial meat production than documentaries such as Cowspiracy and Food, Inc, and its release on Netflix this summer came at a time when, more than ever, consumers are questioning their eating choices, for reasons both medical and environmental, economic and ethical. And just as burgers are always getting tastier, the case against eating them is getting stronger.

Most of us comfortably ignore the inevitable unpleasantness involved in delivering a rump steak or a pork rib to our plates. But if you measure animal cruelty by scale of food production, then there’s no question. It’s growing. Today, all but 12 counties in England have at least one intensive, industrial-scale livestock farm. There are 16 million factory-farmed animals in Herefordshire alone, a county of fewer than 200,000 humans.

Brexit may hasten a move towards US-style meat production, as the recent controversy over the possibility of American chickens on British supermarket shelves demonstrated. EU standards guard against the import of meat washed with chlorine, a process that implies an unacceptably low standard of animal welfare. Major US food producers decontaminate chicken carcasses with chlorine before they go to market because it’s cheaper than instituting health and welfare safeguards earlier in the process.

Ethical questions aside, says food safety expert Professor Chris Elliott of Queen’s University Belfast, chlorine washing has proved to be an effective method of dealing with common, sickness-inducing bacteria such as campylobacter. “But as we look to the future,” he says, “there’s the potential for superbugs that are resistant to chlorine. And what are we going to do then?”

A recent report from the House of Lords, the second chamber of British Parliament, warned that, to secure trade deals with countries such as the US after Brexit, the UK may have to adopt lower food production standards. “The government’s wish for the UK to become a global leader in free trade is not necessarily compatible with its desire to maintain high animal welfare standards,” it stated.

According to the US Centers for Disease Control and Prevention, there are some 50 million cases of food poisoning in the US every year, meaning one in six Americans will get food poisoning in 2017. The risk is closer to one in 100 in the UK. “The EU has developed one of the safest food systems in the world over several decades,” says Professor Elliot. “If the UK moves away from that system, I struggle to see how we could achieve better food safety standards without huge investment.”

Food poisoning can also be caused by fruit and vegetables, but there are clear health benefits to a plant-based diet. Studies show vegetarians tend to have lower blood pressure, and are at less risk of obesity, heart disease, cancer and diabetes than omnivores. The World Health Organization classifies processed meat as carcinogenic and red meat as “probably” carcinogenic. Harvard Medical School recommends eating no more than 100g of red meat per week.

But while the health and ethical arguments against meat eating may be the most persuasive, perhaps the most urgent is the environmental case. The UN Food and Agriculture Organization estimates that livestock farming accounts for almost 15 per cent of manmade greenhouse gas emissions. By 2050, the world population is expected to grow by another two billion and global meat consumption by 75 per cent. Mr Al Gore, the former US vice president and climate campaigner, has been vegan for five years for environmental reasons. And yet, remarkably, the vaunted Paris climate change agreement makes zero mention of agriculture or meat production.

“Food was always excluded from those climate talks because it’s a touchy behavioural subject,” says Dr Marco Springmann, a researcher on the Future of Food Programme at Oxford University. “But it’s now fairly clear that food consumption has to change to a degree for countries to remain within [emissions limits set by] the Paris agreement. The policymakers are waking up to that fact.”

Red meat is the worst offender. One 2014 study found that beef production takes up almost 30 times more land than chicken or pork and creates five times as many emissions. Livestock worldwide are fed enough grain to satisfy the appetites of 3.5 billion people. The average cow produces some 700 litres of methane every day, the same as driving 35 miles in a 4x4. Ditching meat might actually be a more effective way to reduce your carbon footprint than selling your car.

Research suggests meat-rich diets (those that feature more than 100g of meat per day) generate almost twice as many carbon emissions as vegetarian and pescatarian diets. But if you’re going to switch to fish, that also requires discernment. Choose cheap, plentiful mussels over prawns, which are often farmed using unsavoury methods. Buy cans of sardines and anchovies, not endangered tuna. Avoid overfished Atlantic cod in favour of hake, salmon or trout.

Is a meat-rich diet more expensive than a plant-based diet for the average consumer? That question has never been satisfactorily settled, says Mr David Robinson Simon, author of Meatonomics. “Given the heavy levels of subsidy for animal production in most developed countries, and the relatively modest levels at which we subsidise fruit and veg production, if you were to level the playing field, then a vegetarian diet would become a whole lot cheaper to the consumer than meat.”

Mr Simon claims the cost of meat is kept artificially low – in the US and elsewhere – by government farming subsidies, regulation and a disregard for its environmental and health costs. If the meat industry were burdened with the true cost of its production, he calculates, a £3.19 Big Mac would cost £8.60. US politicians are more prepared to subsidise animal agriculture “than any other industrial sector, including oil and coal production”, he says. “It has a lot to do with historical and cultural attitudes, ingrained notions that we need meat for protein and that eating lots of meat is good for us.”

In a study published last year, Dr Springmann and his colleagues estimated meat consumption at current levels could cost the global economy $1.6trn by 2050, much of it spent treating diet-related diseases. The solution, he and his co-authors proposed, is taxation. For instance, in high-income countries, taxes of 40 per cent on beef and 20 per cent on milk. The taxes would not only stop people eating as much meat, but could also provide revenue to subsidise healthier foods.

Experts point to the tobacco industry, which several decades ago still claimed smoking had health benefits, but is now heavily regulated in both its production and consumption. There are other precedents, says Dr Springmann. In 1972, the Finnish government began a broad programme, which included public policy, health services and media efforts, to reduce saturated fat consumption in its North Karelia province, at a time when Finland had the world’s highest cardiovascular disease (CVD) mortality rate. Within five years, the region’s CVD mortality was down 73 per cent.

“It is hard to effect wide dietary changes without regulation,” says Dr Springmann. “You can always talk to individuals and it’s great if they change their diet based on information, but on a population level, the provision of information is usually not enough. People have known since the 1960s that smoking leads to lung cancer, but it’s only now that we see the amount of smoking really dropping. If you’re serious about changing diets, you really have to change the food environment.”