This warning was issued by United States registered dietitian Diana Rodgers, who passionately argues that when it comes to sustainable food systems, the nutritional argument trumps everything.

Ms Rodgers, who co-authored the renowned book Sacred Cow, says removing access to meat is moral and cultural imperialism.

A vegan diet is a privileged diet, she says.

"Go ahead and eat your vegan diet if you live in LA or in a place where you have means and access to all the expensive foods needed to support a healthy vegan diet but don't tell poor people they can't have access to meat because you don't like how it's raised," she said.

Speaking at the recent Global Roundtable for Sustainable Beef conference in Denver, Colorado in the United States, Ms Rodgers said the dramatic difference between fossil fuel emissions and the natural biogenic cycle that cattle are part of was not being taken into account.

Nor the fact that grazing animals make protein on non-arable land that can't be cropped, and that they 'up-cycle' nutrients.

"For every pound of plant-based protein produced there are four pounds of fibrous waste produced that can either sit in a pile or be fed to a ruminant and upcycled into B12 and iron for humans," she said.

"Those type of arguments can be made endlessly. Meat is essential for sustainable and ethical food systems but the nutritional argument trumps everything else."

Meat contains vital nutrients for cognitive development. Women and children in particular require the nutrients in meat, Ms Rodgers said.

"Nutrients like vitamin B12 is not available in plants and if lacking in a child's diet can cause permanent brain damage," she said.

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Ms Rodgers, who has become a well-known advocate for including beef in diets, said she was not funded by cattle industry groups.

She was driven by what she saw as the spread of nutritional misinformation in anti-meat and vegan rhetoric.

"I saw how, in dietetics education, it was considered acceptable to be a vegan or vegetarian but other diets where a total food group is pulled out are definitely not supported," she said.

"As I watched the debate shift into how are we going to feed the world moving forward, it seemed all roads were pointing at plant-based and virtue signaling.

"There was a need for someone to scream that this diet that humans evolved by eating with unprocessed meat and plants also happens to be the most sustainable."

Asked about where she stands on grassfed versus grainfed beef, Ms Rodgers revealed she was once 'cancelled' from speaking at a conference in England because it was for pasture based livestock and she could not advocate that only grass fed beef is good.

"There are, of course, better and worse ways to produce all kinds of food but there is also this sticky little problem around how are we going to feed poor people," Ms Rodgers said.

"We can still advocate for a more sustainable system but we have to ensure that people who don't have access to the one per cent of grassfed regenerative beef produced still have access to healthy nutrients."