I eat all day long, I have a very varied and balanced and healthy diet, but its very structured and disciplined, says Madeley, who manages by giving herself a break from the regime every few weeks. You get three weeks of not drinking at parties, not sharing the birthday cake at the office and you think: At some point, Im going to have to give myself at least a day off or Im going to get really fed up.

McCann eats 2,000 calories a day in the run-up to a competition, when she is focused on shedding fat and revealing muscle, but her diet will be heavily restricted and precision-calculated. I eat very bland when Im dieting. I count out my food, weigh and measure it. But I dont crash diet, I do it over a long period of time. She worries, however, about newcomers to bikini-body contests relying on very low-carb plans to get in shape fast.

Eating this strictly is not necessarily disordered in itself, but rigid diets can easily be taken to extremes by vulnerable people. A recent spate of stories about anorexic people crediting bodybuilding for their recovery set distant alarm bells ringing. It is easy to see how such a regime might satisfy a need for control.

There is anecdotal evidence of people with eating disorders channeling their fixation into exercise, says Liam Preston, head of the Be Real body-image campaign, launched by a group of charities following a parliamentary report on the crisis in young peoples body confidence. They can get obsessive about going to the gym, rather than obsessing about eating. But thats a mental health problem, so I dont know that exercise solves it.

The broader problem he identifies, however, is people chasing fashions in body shape strong or skinny regardless of whether they are healthy. We see so many crazes online and youll find people who go from one to another, trying everything. Its about trying to build resilience, a feeling that their body is fine the way it is.

The YMCA-led campaign is now working with schools to boost younger childrens body confidence, in the hope that this will make them less likely to seek solutions for imaginary faults in their teens. We always try to go with the message that being happy and healthy is more important than anything else; its not about the way you look. If you want to go to the gym, thats great, but are you doing it for the right reasons?

In fairness, Instagrams fitness queens seem intensely aware of their social responsibilities. They constantly repeat that there is not one right way to look, that followers should be kind to themselves, that it is all about balance.

Its really important, I think, to impress upon your audience the importance of not using social media as a way of comparing us use it as a tool of information, but dont sit there letting it make you feel bad about yourself, says Liveing. She was originally known as Clean Eating Alice, but reverted to her name recently after becoming worried about clean eatings association with faddy, exclusionary diets. Food matters in training, she says, but not excessively so.

Madeley is cheerfully upfront about putting on five pounds over Christmas. She reminds followers regularly that the aspirational images they see all over social media are invariably of fitness models at their competitive peak. (A common tactic is training hard for a photoshoot, then trickling out the resulting pictures over several weeks of posts; that way the public persona stays eternally ripped, even if the model does not.)

Sanderson, meanwhile, insists it is unfair and outdated to accuse magazines such as hers of potentially fuelling eating disorders. We look at wellness in a much more holistic way these days theres much more awareness of mental health and nutrition. We dont have a certain aesthetic Im almost 40, Im curvy, Ive got two kids and I run the biggest fitness magazine in the country. In this months editorial, she stresses that, after a few Christmas parties, her abs are not looking like they did in the issues photoshoot and that is just fine.

But however seriously individuals take their responsibilities, the cumulative effect of scrolling through endless pictures of washboard stomachs can be powerful. While writing this article, I created an Instagram account following only fitness influencers, clean-eating bloggers and the odd celebrity suggested by the sites algorithms once it had detected me behaving like a millennial gym bunny.

My time on fitness Instagram was, admittedly, nicer than my usual social media experience (arguing about Brexit on Twitter). But when all you see all day on your phone is amazing bodies, it is surprisingly easy to get sucked in. On day one, I rolled my eyes at all the posts about sauted kale. After a week, I had been running, cooked a lot of chickpeas and wondered about the hand weights that have spent the past 15 years in the loft.

Arguably, that is no bad thing, given that the biggest threat to the average Britons health is failing to get off the sofa. Many of us need a gentle prod. But the risk of promoting any one shape as ideal is that those whose bodies do not conform naturally can easily be left feeling inadequate. Thank God were getting rid of the stigma that women shouldnt have muscles, that if a woman does she looks like a man. Im so happy were breaking down those barriers, says Madeley. But why do we need to bash other people in order to get there?