The Vamps' lead guitarist, James Brittain-McVey, has told MPs pressure to conform led him to have liposuction to remove breast tissue, aged just 20.
At a committee discussing the impact of body image on physical and mental health, the musician said he wished he had opened up to friends at the time.
And he said no doctor had ever asked if he was sure he wanted to have surgery.
Concerns over weight or body shape can often lead to eating disorders, which are particularly common in teenagers.
Two leading medical organisations have told BBC News GPs are not receiving the right support to treat eating disorders.
Doctors said they needed more time with patients and more specialist units.
Brittain-McVey, 27, said he had started worrying about how his body looked aged 14-15.
At school, he struggled to feel he fitted in - and that led him to the gym, prompted by what he saw advertised on social media and by "big American surf style companies".
"I had one of their shopping bags in my bedroom, of a guy ripped on a beach in Malibu, and I think unconsciously every morning I would think that is what I need to look like," the musician said.
"Social media encouraged me to fall further down that rabbit hole.
"The first thoughts I would have when I woke up in the morning was, 'Should I be eating that, am I going to be able to get to the gym?"'
He described worrying about what he ate aged 15-16 - and by the time The Vamps started, he decided to have surplus natural breast tissue in his chest, a condition called gynaecomastia, removed.
"People presume it was me striving for vanity - but it was pressure to conform to stereotypes and gender constructs," Brittain-McVey said.
"And before I realised it, my whole life was controlled by this chase to look a certain way."
His family was supportive of his decision but he was too embarrassed to tell many of his friends or bandmates.
The government should be "clamping down on advertising", he said, so "bodies represent society and not unachievable bodies".
"I worry about future generations," Brittain-McVey said.
"How on earth are they meant to feel comfortable within their skin if you go on apps now and you scroll and see another person that looks a certain way?"
Cosmetic-surgery adverts are to be banned from targeting children in the UK, from May.
Asked if any doctors had discussed with him why he wanted liposuction, Brittain-McVey said: "Before surgery, I don't think anyone said, 'Are you sure?'"
In 2018, he joined ITV's I'm a Celebrity...Get Me Out Of Here! and came out of the Australian jungle having lost 4-5kg (11lb).
"My wife was shocked how ill I looked - but I was happy I had a six-pack again," he said.
The programme had been "brilliant" - but it had made him focus on the way he looked "more than ever".
"I still feel a pressure to look a certain way and that's why I worry for a lot of our fan base," he told the MPs.
The committee is considering whether NHS training on body-image issues should be changed and whether there is enough support, advice and regulation to ensure patient safety.