There's an old joke. 'How do you know if your friend is vegan? Don't worry, they'll bloody tell you'. This year's Fringe is brimming with comedians keen to do just that: explain why veganism is the best thing since sliced (possibly gluten-free, pumpkin-seeded) bread. And hopefully they'll make it funny too.

Veganism has been trending hard recently, and earlier this year, Simon Amstell's BBC mockumentary Carnage did an excellent job of pinning down the zeitgeist, with his very funny sci-fi look at an empathetic utopia, where people attend therapy groups to soothe guilty souls about their carnivorous pasts. Amstell's enlightened interest in Buddhist ideas of compassion and inner-peace beams serenely through footage of pally marketing campaigns from Captain Birdseye, passionate sausage-waving from Jamie Oliver and women turned on by eating yoghurt.

The new agey tone fits brilliantly, and Amstell has a lot of fun taking the piss out of veganism's smugger tropes, but the nods to spirituality hint at something deeper going on in certain areas of the growing vegan community. Those who avoid eating things that once had faces often share some blissed-out philosophies too.

Take 'woke AF' London stand-up Carl Donnelly, for example. During a period of intense unhappiness five years ago, Donnelly smoked the hallucinogen DMT (he's not recommending it, he adds), but thanks it for changing how he looked at the world. 'I know how strange it sounds but I'm so much happier now. I was dabbling in the esoteric, and my subconscious seemed to know that eating meat was making me miserable.' So he swapped his nose-to-tail diet of offal, liver and hearts for one where he now cooks his own vegan 'smoked salmon' using carrots and seaweed.

'I grew up in a council house and my family are proper meat and two veg. They assume I spend about 200 quid on vegan food, when actually I'm shopping down the Middle Eastern greengrocer, making 30 quids-worth of veg and pulses last all week.' Being vegan seems to Donnelly like 'a stamp on the middle-class passport', which makes him cringe, but also gives him plenty material for his show.

Brooklyn comedian Julio Torres is also uncomfortable with veganism's bourgeois image. 'In the States there's this assumption vegans are wealthy, Hollywood types who hang out in spas and gyms. Vegan restaurants are way more expensive too.' The Saturday Night Live writer is more a cheap-bagel kind of guy (his local Bushwick deli now serves 'The Julio', his favourite of tofu cream cheese and vegetables), who also went vegan during an unhappy phase. 'I didn't have a job, I felt directionless and stressed. I wanted to clear my head and simplify. Part of the joy of being vegan is removing choice and thriving within limitations.' The El Salvador-born comic says he's never been religious, but veganism is his attempt to control the choices he makes and define his identity.

Learning what's off-limits is quite an education. McCoy's steak and chicken crisps are fine apparently, but vegetarian Percy Pigs, bananas and orange juice often contain parts from a sentient being. And that's not even getting into the more hardcore territory of those who avoid laptops (made with animal glues), mattresses (containing silk spun by spiders) and fossil fuels (compressed dinosaurs).

Sara Pascoe / credit: Matt Crockett
Aware of the joyless stereotypes about vegans, comedian Sara Pascoe wants to debunk a few, with the following blurb on her website. 'While some people can have preconceptions about what vegans are like (preachy, judgemental, angry, paper thin with no energy), it is the thing I like most about myself. And every day, I feel I do an incremental, very small piece of goodness.' Frustrated by industrial farming and animal cruelty, Pascoe gently evangelises that full veganism is not essential for those who share similar feelings: 'you must feel powerful, even if you simply start by having occasional vegetarian meals or something.'

Pascoe's friend and fellow comedian Jessica Fostekew raves about feeling healthier since going vegan, but takes a flexible approach to it all. On holiday in France, she confesses, 'there's no way I'm going without cheese for a week. I don't react well to absolute rules. It doesn't have to be rigid. But I find it exciting discovering all these amazing substitutes and delicious Thai, Mexican and Indian recipes. Fake bacon is pretty rancid, but tofu has been relatively revelatory.' Fostekew reckons the main moaners about veganism are, 'bitter, grumpy, old white male comedians' who don't embrace change very easily.

Dave Chawner, a vegan comedian whose previous shows have dealt with masculinity, mental health and anorexia, says he wants to be 'balls to the wall honest' with his Fringe show, C'est La Vegan. 'It's hard to make it funny when you're passionate and angry about the environment, or linking veganism to the Big Bang or existential philosophy, which I do. But actually, being vegan is really just about being open to improving yourself.' Chawner admits it's a tough lifestyle choice, summed up neatly by Romesh Ranganathan, who he was backstage with recently at Brighton's Komedia club: 'yeah man, it's hard! Dairy is the shit!'

Thankfully for those comics heading to the Fringe, the consensus is that Edinburgh has plenty good options for vegans these days with Hula, the Mosque Kitchen, Holy Cow and Jordan Valley all getting a thumbs-up. Whether Fringe crowds will stomach this banquet of right-on comedy remains to be seen, but hopefully the vegans are about to convert carnivores to the idea that it's not all puritanical stuff: vegans can have a GSOH too. Or as Amstell puts it, 'I'm not an activist, I'm a clown'.

Carl Donnelly: The Nutter on the Bus, Heroes @ Bob's Blundabus, 3–27 Aug (not 9, 16), 7.30pm, £7 (£6) or Pay What You Want.
Dave Chawner: C'est La Vegan, Laughing Horse @ The Counting House, 3–27 Aug (not 25), 7pm, free.
Jessica Fostekew: The Silence of the Nans, Just the Tonic at the Caves, 3–26 Aug (not 14), 4pm, £6 (£5) or Pay What You Want.
Julio Torres: My Favourite Shapes, Underbelly Cowgate, 5–27 Aug (not 14), 5pm, £9.50–£10.50 (£8.50–£9.50). Previews 3 & 4 Aug, £6.50.
Sara Pascoe: LadsLadsLads, Pleasance Courtyard, 5–27 Aug (not 14), 7pm, £10–£13 (£9–£12.50). Previews 2–4 Aug, £7.
Simon Amstell: Work in Progress, Pleasance Courtyard, 17–19 Aug, 11.20pm, £15.