British actress Lily James stuck to a liquid diet while shooting new Disney movie Cinderella because her corset was tied too tight for her to properly digest solid foods.

The Downton Abbey star took on the titular character in Sir Kenneth Branagh's live-action adaptation of the classic fairytale, but she admits she had to suffer for her art to ensure she didn't burp in the face of her Prince Charming, played by former Game of Thrones actor Richard Madden.

She tell, "When (the corset) was on, we would be on continuous days, so we wouldn't stop for lunch... You'd be sort of eating on the move. In that case, I couldn't untie the corset...

"If you ate food, it didn't really digest properly, and I'd be burping all afternoon in (Madden's) face, and it was just really sort of unpleasant. I'd have soup so that I could still eat but it wouldn't get stuck (sic)."

James' diet secrets emerge after she was forced to dismiss suggestions movie bosses digitally altered her onscreen image to give her a smaller waist, insisting no computer-generated imagery (Cgi) was used to make her appear more slender.

She recently told the Los Angeles Times, "I naturally have a really small waist. The skirt's big and the corset pulls me in and that's the point. That's the shape (the costume designer) created... I think it's a beautiful gown with a beautiful shape...

"I think it's all very hypocritical... and they're drawing more attention to it... I think all that stuff's so negative, and you've got to let it wash over your head. I'm so healthy. I've got hips and boobs and a bum and a small waist."