It has been known for a while that the amount of animal products being eaten is bad for both the welfare of animals and the environment. People cannot consume 12.9bn eggs in the UK each year without breaking a few.

But the extent of the damage, and the amount by which people need to cut back, is now becoming clearer. On Wednesday, the Lancet medical journal published a study that calls for dramatic changes to food production and the human diet, in order to avoid “catastrophic damage to the planet”.

The study sets out the targets for a daily diet to “place consumption within the boundaries of the planet”. They include a reduction in red meat consumption of more than 50%, and a doubling of the intake of nuts, fruits, vegetables and legumes. “But in specific places the changes are stark. North Americans need to eat 84% less red meat but six times more beans and lentils. For Europeans, eating 77% less red meat and 15 times more nuts and seeds meets the guidelines,” wrote The Guardian’s Damian Carrington.

Others have called for even more drastic changes to human diet to be made. Another study, published in Octoberin the journal Nature, estimated that meat consumption had to be reduced by 90% to avoid unsustainable global warming, deforestation and water shortages.

Facebook Twitter Pinterest A chef preparing meat in Buenos Aires. A study is calling for a 50% reduction in intake. Photograph: Ronaldo Schemidt/AFP/Getty Images

Whatever the figure, there is a growing consensus that a drastic reduction in overall meat consumption is needed to maintain the health of the planet. What is not clear is how that will be achieved.

Excessive meat consumption, like other environmental crises, needs political solutions. Yet most discussion about whether to eat meat remains rooted in personal choice. So far the biggest change in our diets has come from a small but increasing percentage of people who identify as vegetarian or vegan: their answer to a global crisis is to swap out beef for cauliflower steak.

The trend towards a meat-reduced diet is largely being driven by young people. A study released this month by the analysts Mintel found the UK has overtaken Germany in the number of new vegan products brought to market. Another agency, Acosta, found 26% of millennials are currently vegetarian or vegan.

But by just focusing on personal consumption, a paradoxical situation has emerged where the number of people who consider themselves vegetarian has risen, but so has overall meat consumption because the population of the world is increasing, and many people who do eat meat are eating more of it.

That is why many are now calling for a shift in approach: towards a regime that can involve more people and be less rigid about the rules of meat consumption. Sometimes given the slightly clunky titles flexitarian or reducetarianism, advocates of this approach are not especially bothered if you eat a bowl of chicken soup every now and again. What is more important to them is encouraging people to think about what they can do to reduce meat consumption worldwide.

One of the leaders of this movement is a man called Brian Kateman, who coined the term reducetarian and now runs a foundation bearing that name. Speaking to the Guardian via Skype, he paces his office eating a bowl of vegetables from the salad chain Sweetgreen. He says there is no one thing behind his desire to motivate people to eat less meat: he is worried about heart disease, animal cruelty, high food prices and environmental destruction. Reducing meat intake can solve a lot of problems, but he says people need to be less puritanical.

Facebook Twitter Pinterest Brian Kateman. Photograph: Andrei Severny

His own inspiration came from a bout of sibling score-settling. “I remember one Thanksgiving, I ate a small piece of turkey and in that moment my sister, as siblings will do, said to me: ‘I thought you were a vegetarian Brian.’ I couldn’t articulate then as well as I can now, but I thought about how the average person in the developed world eats around 200lb [90kg] of meat a year, and I’m eating let’s say 5lb of meat a year. That’s a lot better. We need to be mindful of how challenging that can be for people and we need to create systems where the default choice is the moral one.” Brian also says that not all meat is the same. High quality, organic meat produced in cruelty free conditions is preferable.

The foundation he set up aims to encourage society at large to reduce its intake. “We’re used to thinking about food as a personal choice so in our brain we’re accustomed to it being in this different category. But once you understand that factory farming and the products it produces are so connected to so many issues that are detrimental not just to ourselves but to others, it allows us to recognise that what comes out of your mouth is just as important as what goes into your mouth.” He suggests supporting policy initiatives and encouraging restaurants to broaden their menus as small actions that can help.

Facebook Twitter Pinterest The UK consumes 12.9bn eggs each year. Photograph: David Levene/The Guardian

While there has been some light government intervention around food when it comes to personal health, including improvements to school dinners and the levy on sugary drinks, food ethics has traditionally been outside the realm of parliamentary politics.

Dr Marco Springmann, who led the research group that published the report in Nature, says the stakes are too high for politicians to remain squeamish about regulation. “Just yesterday I had a meeting with civil servants from Defra [the Department for Environment, Food and Rural Affairs] and they were commenting that dietary change is a contentious topic and politicians don’t want to get close to that. We saw similar statements from some politicians after we released the report. I think they’re just so afraid of not being electable if it appears to be trying to prescribe what people eat. If there is not a substantial change within society first, politicians won’t lead the way because it’s too controversial.”

He says he is hopeful there will be a groundswell of change, particularly in big cities where restaurants specialising in plant-based dishes are popular. But millennials cannot make the change on their own. “The challenge is to make it not only a very trendy thing for young folks but also to make it accessible for the older generation.”

A big problem with relying on vegetables becoming increasingly fashionable, though, is that it is a global issue that needs a global solution. Even if it becomes cool to eat less meat in western metropolitan cities, will that offset increases in meat consumption elsewhere in the world? Since the death of Mao Zedong in 1976, pork demand in China has increased by an average of 5.7% each year. It is now the biggest per-capita consumer of pork products in the world.

Facebook Twitter Pinterest A customer builds a salad at a supermarket in Los Angeles. Photograph: Bloomberg via Getty Images

But Springmann says small local changes can still have a global impact. “If you look at why people in China eat the way they eat, for one they have a huge rise in income levels so they can afford more meat, but why do they even want to eat meat? Well they very often look towards the west to see what rich people eat,” he says. “If you talk to a Chinese person and you say you’re vegetarian for example they don’t get it. But if there is a large enough group that eats that way and it’s clear that it is progressive rather [than] a sacrifice, then it would be a strong signal to rapidly industrialising countries like China that want to catch up.”

Even in the west, people switching from animal to plant products does not necessarily mean an immediate reduction in meat and dairy production. In the US, a decrease in dairy consumption has led to lower milk prices, meaning that farmers are now overproducing to try to offset their loses. Thousands of gallons of unwanted milk have been turned into processed cheese and is sitting in warehouses across the US, uneaten.

May I have a word about… flexitarian diets | Jonathan Bouquet Read more

But there are reasons to be optimistic. In California, campaigners petitioned for a ballot measure that would make intense factory farming of caged chickens illegal. It passed during the most recent midterm elections and although Peta and others say it does not go far enough, itis a step in the right direction.

If, in the UK, councils fine people for not recycling and high-emissions cars can be banned from the centre of London, it is time for individuals, companies and governments to actively work to reduce people’s meat intake, whether they want to or not, campaigners say.

Springmann says if we do not get over our squeamishness about making these changes quickly, things are going to get a lot worse. “If we continue with our current levels of meat consumption, it’s very likely that we will have more flooding, more hurricanes, extreme weather that is associated with exceeding the two-degree target for climate change ... if nothing is done then those pressures could increase by 50 to 90% and by that time it will basically exceed all environmental limits or so-called planetary boundaries that define a safe operating space for humanity.”