Taylor Kitsch was ''f***ing stupid'' to lose so much weight for a movie role.

The 30-year-old actor - who is a trained nutritionist - shed 35lb in just two months to portray war photographer Kevin Carter in 'The Bang Bang Club' and he hated the effects the rapid weight loss had on him.

He said: ''I lost 35lb (15.8kg) in two months. That was f***ing stupid and there's not a lot of actors who will do that. It's just way too extreme, and being a nutritionist I found it hard. Everything I knew just went out the window.

''The way I worked, it changed my walk, my confidence, everything. I was very bipolar. My mood swings were f***ing insane. I was very emotional, I had night terrors, I couldn't sleep. It was a zoo.''

But Taylor always puts everything into his work because he hates the thought that someone might be disappointed by his efforts.

In an interview with the new issue of Men's Health magazine, on sale March 5, he added: ''The worst feeling in the world is doing something and people thinking, 'Ah, he could have worked harder.'

''In the end it's about energy. If you put half your energy into something, you're only going to get that back at the end of the day. But I'm like, 'What if I put in f***ing everything without any other variable?' That's what I was like for John Carter. I was like, 'OK Kitsch, let's see what you can do.' Just give it everything.''