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 mad. 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.

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.

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.