Can a polemic be subtle? If so, the new documentary Planeat, is almost that rare beast.

The polemic is against eating meat. Cleverly interspersed between scenes of ornate and beautiful vegetarian food being prepared in aspirational restaurants, scientists appear to explain why they think eating animals, and their products, is a bad idea.

It's bad for your health, argues T Colin Campbell, a Cornell professor and leader of the landmark China study, which revealed the impact of meat and milk heavy diets on westerners. Whether his research on rats showing that casein turns on or off cancer when included or excluded from their food has any relevance for humans, I don't know. Campbell is supported by medical doctor Caldwell Esselstyn, who claims his vegan diet halts heart disease, though there's no mention of any control studies.

It's bad for rivers and oceans, says Gidon Eshel, at Bard College. He takes on the direct environmental impact of intensive farming, in particular the flow of nitrate pollution into rivers and the oceans.

And it's bad for the planet, says Eshel again, showing how much more greenhouse gas is generated in raising a meat-eater's menu compared to a vegetarian's. "Most people have no greater spatial effect than their dietary choices," he says. Given that eating crops is clearly more efficient than eating the animal that eats the crop, that's seems pretty uncontroversial to me.

In the end, the argument made is pretty simple. Global population is growing, meaning more mouths to feed, even if the dreadful inadequacies of existing food distribution is overcome. So we need more food, but meat has a very heavy impact on the planet, both directly and via greenhouse gases. So if we all want to sit down to eat without killing ourselves or the planet, we in the west will need to eat less meat and dairy.

I find it hard to fault the logic in that, and I am not alone, with the Intergovernmental Panel on Climate Change chair Rajendra Pachauri, economist Nick Stern and the United Nations Environment Programme agreeing. I'm not going to become a strict vegetarian, at least not yet, but I have given up meat at lunch. Big deal, you might say, and you might be right, but it all helps, and thanks to our nice office canteen, I don't feel deprived at all.

Planeat is released in the UK on 20 May.

Note: I fixed a typo in Eshel's quote. It originally said: "Most people have no great spatial effect than their dietary choices."