TV writer Kay Mellor has revealed how researching her acclaimed series Fat Friends led her to become "fixated" on losing weight.
Mellor has also told of her shock at learning she had become pregnant at the age of 16 "literally the second time I'd had sex".
The 66-year-old, who has turned Fat Friends - which aired from 2000 until 2005 - into a musical, said she was told by a slimming group leader that she needed to lose two stone, despite only going along for research purposes.
Mellor told BBC Radio 4's Desert Island Discs host Kirsty Young: "Everybody I spoke to was on a diet, the cabbage soup diet or whatever.
"It was before the 5:2 diet, so they were on Slimming World, Weight Watchers, there were a million diets out there, and I'd look at people and go: 'Why are you on a diet, you've got the most gorgeous figure?' And they'd go: 'I've got to lose five pounds.'"
Mellor said she attended a slimming group - wearing "really heavy clothes and big shoes" and with her pockets "full of heavy things" - and was surprised to be told by the slimming club's leader that she was considered to be overweight.
She said: "I stood on the scales, she looked at me and I looked at her and she said: 'We'll start half a stone at a time.'
"And I went: 'Sorry?' - looked down at the thing - and she said: 'You're two stone overweight.'"
Mellor continued: "But then, slowly, I became fixated, myself.
"I started to want to lose weight so I could please her and please all the class and stand there and be applauded for losing the weight."
Bafta-nominated series Fat Friends, which focused on the members of a slimming group in Leeds, starred James Corden, Ruth Jones, Alison Steadman and Mellor's youngest daughter, Gaynor Faye.
Mellor chose The Beautiful South's Perfect 10, the Fat Friends theme tune, as one of her Desert Island Discs, because "every time I heard that I used to get excited and get butterflies".
She said: "It was such a lovely time of my life, it was a drama that was really important to me because I thought I had something to say about weight and body image."
Mellor, who is behind a number of successful TV shows including Band Of Gold and Playing The Field, told Young about how she and her husband Anthony were "bewildered" when she fell pregnant at such a young age with their eldest daughter, Yvonne.
"I didn't know anything, really, I was so naive," she said.
"Literally, the second time I'd had sex I was pregnant, because I'd never heard of the pill, and then for ages I was missing my periods and I didn't even realise I was pregnant."
Mellor said she was later told by a doctor that she was four and a half months pregnant and that she and Anthony decided to keep the baby and get married.
They held their wedding at a registry office, because their vicar had refused to marry them because he thought they were "too young and that it wouldn't last".
This year marks the Mellors' 50th wedding anniversary.