For climatarian Donna Collins, 38, it was a documentary that made her change the way she ate for ever. ‘It just highlighted how damaging modern farming is in so many ways,’ says Donna, an architect and owner of online interiors store Domo.

‘Areas that used to have ancient forests and beautiful, diverse wild plants are now just depressing squares of grazing pastures, and I simply couldn’t continue to turn a blind eye.’ 

In the six years since, she’s cut out meat entirely, swapped dairy for oat milk, and focused more on buying organic to reduce the impact of pesticides on the land. As well as being more content about her place in the world, she says she’s never felt better.

It’s billed as the diet that will help save the planet – and also turn around your own health. And the climate-friendly way of eating has gone so mainstream that everyone from health experts to fast-food chains is leaning into it. So what is climatarian eating, and why is it bad news if you like avocados?

It’s not just another way to say ‘vegetarian’ or ‘vegan’ – although that may be part of it. ‘It means eating to reduce all elements that contribute to a food’s carbon footprint – which also means considering the amount of processing involved, how far it’s transported and how much of it you buy or waste,’ says Dr Alona Pulde from nutrition app Lifesum, which is increasing the climatarian advice offered to its users. 

If you’re eating to save the planet, local, seasonal, unprocessed and plant-based foods are in; meat, dairy and water-intensive crops like avocados are likely out.

It’s estimated that 34 per cent of the world’s man-made greenhouse-gas emissions are linked in some way to the food we eat. ‘It’s astonishing that there is not massive discussion on this,’ says Timothy Lang, emeritus professor of food policy at London’s City University. 

‘It was barely even discussed at COP26. That’s not to say coal and deforestation aren’t important, but what drives deforestation is food production and if we want to have any chance of meeting net-zero targets by 2050, it’s an issue we need to address.’

The climate-friendliness of a food can be determined by analysing a huge range of factors, such as how much power is used in making or storing it, and how much water is used growing a crop or, in the case of meat, cleaning a factory or farm.