She might feel pretty, but we can only feel pity for Amy Schumer right now. On one level, that’s the appropriate response. In her new movie, Schumer’s character, Renee, strips down to her Spanx, sighs at her un-toned figure in the mirror and wonders how she’s ever going to attract a mate in today’s image-obsessed world. But one blow to the head later, Renee suddenly sees herself as utterly gorgeous. And with this newfound confidence, her life starts to fall into place, even if we, the audience, are still laughing at, rather than with, her.

The premise has left a lot of people scratching their heads. One Twitterer summed it up: “As someone who looks considerably less attractive than @amyschumer in a bikini, has considerably less middle class privilege, & a chronic illness – what am I supposed to take from #Ifeelpretty – that I’m hideous to society and need brain damage before I can believe in myself? Ffs.”

There’s also the uncomfortable fact that Renee’s closing, motivational “we’re all beautiful inside” speech is folded into her triumphant launch of a new cosmetics range. Faced with these reactions, Schumer has found herself not so much promoting I Feel Pretty as defending it. “It’s not about an ugly troll becoming beautiful,” she recently explained to Vulture, “it’s about a woman who has low self-esteem finding some.”

Again, it’s a pity, considering the sharp body-image comedy Schumer regularly served up in her sketch show Inside Amy Schumer. Like parody boyband song Girl, You Don’t Need Makeup, which highlighted the exact hypocrisy I Feel Pretty peddles (the song concludes with the boys deciding that, actually, she does need makeup). Or there was her undercover detective, Plain Jane, whose frumpiness makes her literally invisible to Miami’s hot-bodied criminals. “Goddammit, Plain Jane! If only inner beauty mattered,” her boss says. “I wouldn’t be half the cop I am today, Chief,” she replies.

I Feel Pretty has already borne comparisons to the Farrelly brothers’ 2001 comedy Shallow Hal, in which the magical ability to see inner beauty is acquired by a sexist skirt-chaser, played by Jack Black. As a result, he is smitten by a morbidly obese woman because, to him, she looks like Gwyneth Paltrow. She is Gwyneth Paltrow – except, to everyone else, she’s Gwyneth Paltrow in a fat suit, literally throwing herself into weight-shaming gags (she jumps into a swimming pool; the water jumps out). Through Hal’s eyes, we see her as the real, perfectly thin Gwyneth Paltrow pretending to be insecure about the obesity problem she clearly doesn’t have. Neither is a good look. Perhaps the real problem is that “inner beauty” is something that movies, being a visual medium, are traditionally very bad at communicating. Many of them simply translate inner beauty into outer beauty – or a narrow, classical definition of it.

Physical beauty is readily equated with virtue, and ugliness is evil, as with the scarred villains of James Bond or Star Wars or The Lion King. You’ve got your ugly duckling/Cinderella narratives, such as The Princess Diaries, Never Been Kissed, Miss Congeniality, Audrey Hepburn in Sabrina, Audrey Hepburn in Funny Face, er, Audrey Hepburn in My Fair Lady. All of them do the same thing as Shallow Hal: get an attractive actor, fugly them up, then de-fugly them and say: “Why, you’re beautiful!” What these movies are saying is inner beauty is great but it’s not enough.

There are exceptions to the rule: David Lynch’s The Elephant Man, or perhaps the soon-to-return superhero Deadpool, whose horribly scarred face is by no means a deal-breaker for his girlfriend. But if you’re looking for a film that radically challenges assumptions about inner and outer beauty, the fairest of them could well be Shrek, which merrily turns all those fairytale beauty myths on their heads, especially the one about “love’s true form”. For the cursed princess Fiona, this is not her shapely human princess body but her outsize, green-skinned, trumpet-eared ogre one. Admittedly it’s an animated fantasy, but Shrek succeeds where I Feel Pretty fails – in challenging definitions of beauty with a deft sense of humour, and without the need for head injury.

I Feel Pretty is out now