The Oscar-winning actor, 38, said women tend to be "valued" for their appearance.

She told Harper's Bazaar magazine: "As a woman, you are constantly fighting against only being valued for your looks, because it becomes a very tenuous thing, to be defined by the gaze of others, the opinion of others.

"And beauty is, by definition, ephemeral, it's a thing that you can't trap in time, it's a butterfly, it lives for a second.

"So to make a lifetime worthwhile and have meaning cannot rest on beauty."

Portman also said she feels women have been "socialised to believe that we're not feeling angry - we're feeling sad, we're feeling upset".

She said: "And when I realised that, there was a sudden shift in my mind, and I thought, 'Oh my God, all those times when I would burst into tears, I was actually angry!'

"I just didn't know how to express it!"

The actor's latest role is as an astronaut in Lucy In The Sky, which was produced by Reese Witherspoon.

Explaining how she chooses her film roles, the mother of two said: "I just feel weird if I'm at work pretending to be a mom to some kid who's not my kid.

"So I've been trying out wild experiences like being an astronaut or a pop star."

Australian Associated Press