Last week, after a cancer benefit honouring her doctor friend, the singer Pink shut down critics who said she had gained weight with a tweet declaring that she felt beautiful and secure. It was a rare moment: a celebrity openly acknowledging the trolls, straight from her phone, then choosing to ignore them and look after her “healthy, voluptuous and crazy strong body” instead.

Pink’s mainstream use of the word “strong” is worth noting; the mantra “strong is the new skinny” has been gaining currency online among female gym devotees for some time now. Its everyday popularity – popping up on Facebook, slogan shirts and fitness books – signals a move away from “thinness” in favour of a more achievable, “real” body, led not by magazines but by social media.

But social media doesn’t always present reality unfiltered, and to grasp at reason in a sea of Photoshop takes conviction. For all the democratisation that the social web presents, the pictures seen on Instagram, Facebook, Twitter and Tumblr can frequently be as “real” as reality TV. And to maintain a social media presence, celebrity or not, is to offer up one’s body for crowdsourced contempt and constant scrutiny. Instagram, in particular, is a land of the hyperreal, full of Photoshopped thigh gaps and waist trainers (the Kardashian-endorsed take on Victorian-era corsets).

The new brand of body fascism isn’t just about fat and thin: “healthy” now functions as an aspirational hashtag, one arguably more powerful, self-righteous and potentially misleading than “thin” ever managed to be. Fed on a diet of health blogs and images labelled as “fitspo” , we risk confusing what is healthy with what attracts the most clicks.

Psychotherapist, activist and author Susie Orbach notes that relationships with food are now refracted through the Instagram filter: “Food becomes this completely fetishised and privileged thing,” she says. “The basic underlying psychology of it is terror food – something that could do terrible things to the way you look.”

At its most benign, “fitspo” – short for “fitspiration” – provides a gentle, visual nudge to eat more kale and go to the gym on Mondays. At its most dismal, it’s an addictive feedback loop of judgment and self-loathing: take the story of Jess Semmens, who lost 57kg (9st) by “Instagramming herself thin”. Semmens was advised by doctors to lose weight, and her commitment to following that advice involved photographing every meal, posting the images on Instagram and asking for her followers’ approval. Is the “healthiest” diet the one with the most likes? Is it healthy to crowdsource your body image and let the internet take over your real life? Semmens was reported as putting her weight loss down to openly courting peer pressure: “If I didn’t stick to the diet I wasn’t just letting myself down, I’d be letting down all my followers too.”

It is strange to think that diets once undertaken in private – as grim and solitary cabbage soup affairs – are now a visual medium, showcased in mason-jar breakfasts, fridge-shelf snaps and plates of raw “courgetti”. While plenty of people enjoy photographing their food, it seems that with the right combination of good looks and anti-gluten rhetoric, anyone can become a social media superstar.

This same health-conscious culture launched “food activist” Vani Hari, AKA the Food Babe, earning her 87,000 Twitter followers and 939,000 Facebook fans. Hari drew criticism recently after profiles in the New York Times and Gawker revealed that she takes a commission from the products she endorses and bans those who question her credentials (the Banned by Food Babe Facebook group currently has more than 8,500 members).

Hari built her fame on attacking popular food products such as Starbucks’ pumpkin spice latte, Kellogg’s breakfast cereals and Subway rolls, distilling “health” into a series of hashtags: #realfood, #livepure, #cerealkiller and #foodbabeway among them. Her campaigns resemble those of Freelee the Banana Girl, the self-styled “YouTube health guru” from Australia who advocates a carb-heavy vegan diet and fruit fasts. Sometimes Banana Girl’s videos attack other widely followed YouTube personalities; she appeared in court in March after a rival health blogger’s accusations of defamation. Fruit fasts and detoxes may have their detractors, but controversy breeds clicks and has earned Freelee more than 350,000 subscribers on YouTube.

With empires built on unachievable eating, figures such as Freelee, Hari and Maria “Fit Mom” Kang represent fitspo at its most extreme, documenting lifestyles that are followed as much out of curiosity as aspiration. But fitspo can be every bit as tyrannous as the “thinspo” that preceded it – a tag banned from Instagram in 2013 and Tumblr in 2012 for its role in pro-eating-disorder communities. Use of the term fitspo has risen exponentially since thinspo was banned, prompting the question of whether “pro-ana” has covertly gone mainstream, hiding under the cover of Lululemon yoga pants.

Fitspo appears to offer a softer alternative to size zero, a more “womanly” aesthetic embodied in the gym-tight abs and curves of fitness model and Instagram queen Jen Selter. Where thinspo was a life and (often) death pursuit that swapped regular meals for cigarettes, Diet Coke and glorified self-destruction, fitspo takes a more moralising tone, scolding even as it seduces with 6am gym selfies and shots of “clean” meals. The language can be brutally reductive: pain becomes progress, fat deserves shame, weakness is failure and your self-worth is measured by how your body looks.

Fitspo ranges from scaremongering to orthorexic to twee. It it is versatile and deceptive, surfacing in campaigns against Monsanto as well as “my morning routine” videos, where YouTubers breakfast on chia seeds and self-satisfaction. Even the word “real” has been appropriated by hashtags such as “#realwomen”, another act of Manichean hashtag logic, where bodies become either real or fake, fat or thin, toxic or healthy. We need only look to viral news website the Chive’s recent use of one woman’s anorexia recovery pictures as proof of how reductive this logic is: the pictures were used in reverse, as evidence of an “amazing” weight-loss story.

Orbach describes social media as a place where we negotiate our own fears and body insecurities, seeking approval in the follows and likes of others. “We don’t even grow up with a stable body, so we are vulnerable to trying to find one,” she says. “These are attempts to create security where there is none. There is that desperation for recognition, that nobody is able to see their self with eyes that aren’t critical.”

It is a full-time job, this new tyranny of visual health. It sneaks up on you and, if you’re not careful, turns your life into a PR campaign. “What young women and young men have been invoked into doing is creating themselves as a brand,” says Orbach. “What you look like, what you produce, what you say is awesome – all that becomes your identity, instead of actually connecting with people.”