The British actress, 48, revealed she was encouraged by a crew member on her latest film to sit up straighter while wearing a swimsuit because it would look more flattering.
Winslet, who was portraying the photographer Lee Miller in the biopic Lee, told Harper's Bazaar UK about the encounter.
"There's a bit where Lee's sitting on a bench in a bikini ... And one of the crew came up between takes and said: 'You might want to sit up straighter'. So you can't see my belly rolls? Not on your life! It was deliberate, you know?"
Asked if she does not mind looking less-than-perfect on the big screen, she said: "The opposite. I take pride in it because it is my life on my face, and that matters. It wouldn't occur to me to cover that up."
Winslet was just 20 when she found fame in 1995's Heavenly Creatures and 22 when she became a global megastar in James Cameron's disaster blockbuster Titanic.
She reflected on some of the press coverage she received at the time saying, "there was a lot of bullying of me that went on in the media, and that did get to me".
"Look at all those years in my 20s when I was all sorts of different shapes and sizes."
Winslet feels "a huge sense of relief" that women are now so "much more accepting of themselves and refusing to be judged".
"I don't know a single contemporary of mine who grew up seeing her mother looking in the mirror and saying: 'I look nice!'
"My mother never did: it was always, 'Oh God, I don't think I can wear this, do I look hippy, does my bum look big?'
"We waste so much time being down on ourselves and I'm just not doing it ever again."
Winslet refuses to have work done on her face.
"I think people know better than to say, 'You might wanna do something about those wrinkles'.
"I'm more comfortable in myself as each year passes. It enables me to allow the opinions of others to evaporate."
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