Scarlett Johansson has never been known for standing up for women, but she took one for the team the other day when she responded on the Huffington Post to reports that she had lost 14 pounds while preparing for her new role as the Black Widow in Iron Man 2.

Lots of actors, both male and female, get "into shape" for parts. Sometimes they gain weight like Renée Zellweger in Bridget Jones's Diary, sometimes they lose weight, like Christian Bale in Rescue Dawn, and sometimes they buff up like Hilary Swank for Million Dollar Baby and Hugh Jackman for the upcoming Wolverine. Since Johansson acknowledged that she will be wearing a latex catsuit, in her mind (and probably her producers' minds) the workout regimen is warranted, since last time I checked latex catsuits are pretty unforgiving.

Johansson stood up to the tabloids, accusing them of embellishing her weight loss and rightfully reminded the public that many women and girls (and men and boys) struggle with eating disorders. She wants to make sure that those people (especially the young ones) who see and are affected by images of celebrities in popular culture don't get the wrong idea and try to look like her by starving themselves.

Here we find ourselves in a familiar place of berating a female actor for her skinniness, but isn't that very skinniness what we demand of them? I challenge you to think of the last Hollywood film where the women looked normal. I guess a better question would be – do we even know what normal looks like any more? Judging by Hollywood standards, I don't. Thinness is what is expected and demanded of our actors – except when they get too thin, because then they get blasted like Johansson and, recently, Keira Knightley and Jennifer Connelly.

A girl can't win. Female actors are held up to unrealistic double standards. While Johansson felt compelled to up her workouts, she had better make sure that she retains her voluptuousness. The site Joblo.com wrote in response to the weight loss rumours: "As everyone with a schlong anticipates the first image of Scarlett Johansson as Black Widow… If Scarlett did in fact lose 14 pounds for her role as Black Widow, let's just hope they weren't from the chest... or butt." These are the very fans that the movie business relies upon to make Iron Man 2 the same success the first film was. Here's a newsflash for the guys on JoBlo – when you lose weight and your boobs are real you will lose weight from your chest. That's just the way it works. That site illustrates the ongoing problem for female actors,especially the young ones: be unhealthily skinny but have a nice butt and a great rack. No wonder women are having plastic surgery at 22.

For another example of the double standard, look at Russell Crowe in the excellent State of Play, which opens this week in the US. The man is not thin, in fact he's quite portly, yet no one talks about his weight as a career hindrance or a monumental issue. I guarantee that if the genders were reversed and Rachel McAdams's character was the lead, there would be no way that she would have been cast looking the way that Crowe does.

So good for Johansson for talking about an issue near her heart. It would be great if more actors felt comfortable talking about the unrealistic standards they are held to. One example to look to is Emma Thompson, who last year stood up for Hayley Atwell when she was told to lose weight for Brideshead Revisited. She threatened the producers that she would quit if they didn't back off. But we can't expect (though we would welcome) many actors taking up Thompson's or even Johansson's mantle. The film business is just too competitive and the shelf life of female actors is already extremely short. Given those circumstances, why would anyone speak out? This makes the fact that Johansson did even more important.