“Manly man,” the narrator observes, as a groom emerges from a house, carrying his bride. “Calm,” he marvels, as a man in a packed train carriage smiles tolerantly at the lady who just stepped on his foot. And on it goes… a sequence of scenes depicting men carrying out impressively gallant feats, as an orchestral soundtrack rises to a crescendo. At the end of the advert, a man bites into a burger. The tagline reads: “100% manly man. 100% pure beef”.

This McDonald’s advert, broadcast in China in 2012, relies on the well-trodden stereotype that meat is masculine. And oddly, there is actually some truth to this. It turns out that – in almost every part of the globe, from Sweden to Australia – there are significantly fewer male vegans and vegetarians. In the US, one survey of 11,000 people found that just 24% of vegans are men.

Anecdotally, this seems to stand up. The tally of famous female vegans is a glittering line-up, reportedly including – deep breath – Natalie Portman, Miley Cyrus, Venus Williams, Ariana Grande, Ellie Goulding, Jessica Chastain, Alanis Morissette, Jane Goodall, Princess Beatrice and Beyonce.

Meanwhile, the cast of male celebrity vegans appears tiny in comparison, though it does feature Benedict Cumberbatch, Peter Dinklage, Zac Efron, and – notoriously – the singer Morrissey, who masterminded a Smiths album called Meat Is Murder and is said to have forbidden his band members from being photographed eating meat.

More from The Vegan Season on BBC Good Food

But why is this the case?

As it happens, psychologists have been aware of the mysterious abundance of female vegans for decades. They’ve come up with plenty of compelling explanations already – and they don’t reflect well on men.

One possibility involves “precarious masculinity” – the idea that men are constantly worrying they will lose their manly status, and therefore feel the need to prove it at every opportunity. For example, when men are forced to do something “girly”, like braiding a doll’s hair, they tend to want to exhibit their machismo afterwards.