The thrice-married actress revealed she was "curious" in her late teenage years and she could relate to her character in the 1994 movie Heavenly Creatures about the all-consuming and obsessive relationship between two teenage girls.
According to The Telegraph, she told the Team Deakins podcast: "I'll share something I've never shared before. Some of my first intimate experiences as a young teen were actually with girls.
"I'd kissed a few girls, I'd kissed a few boys but I wasn't particularly evolved in either direction.
"But at that stage in my life I certainly was curious, and I think there was something about the really intense connection that those two women have that I profoundly understood.
"I was so immediately sucked into the vortex of that world they were in that obviously became horrendously damaging to both of them. I mean, they murdered someone because they truly believed that that person was preventing them from being together.
"And whilst of course I couldn't truly understand that part of it, I could certainly understand how influenced a young person's mind can become by just one other person when you're so so vulnerable."
Kate - who was 17 when she filmed the movie - revealed the film changed her.
She said: "I know I came back a different person, because I'd evolved so much in my learning and life experience and being in that wonderful country."
The star – who has daughter Mia Honey Threapleton with ex-husband Jim Threapleton, son Joe Alfie Mendes with second husband Sam Mendes and son Bear Blaze Winslet with Edward Abel Smith - also revealed she is uncomfortable with fame.
She said: "I'd much rather be in the shadows of the trees just making art with friends and having a great time that way.
"And the other side of the job, which is the exposure that has come hand in hand with the career that I have had, I've always been slightly at odds with that. I always feel as though fame kind of came and found me - I actually didn't go searching for it, not in an ambitious way."
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