Firstly, I'm very sorry about what you've personally been through regarding eating disorders. That sounds horrendous. Nothing but sympathy on that front.
I still think the nudity in this specific film was artistically justified, but I'm not going to bore you with details. I will agree to disagree. Not everyone has to think the same way, and that is fine. I fully respect your opinion. :)
I will say that in general terms, leaving this film to one side, I agree there are films, TV programmes, music videos, advertisements, photographs, and other images that promote bad body image (whether containing nudity or not). I'm starting to see a shift where a greater variety of body types are included, but that revolution hasn't taken hold fully yet. I hope it does.
I certainly agree that pornography is damaging (that's why I avoid it) but I don't think nudity as a part of storytelling is the same thing. Here in the UK, the British Board of Film Classification (BBFC) talks about the intent of a work - ie, does it exist purely to create sexual arousal? If so, it is defined as pornography. If not, it isn't (and clearly, Oppenheimer isn't). It is this point, where the BBFC (and indeed the rest of western Europe and Scandinavia) are clearly at odds with the MPAA and attitudes in the US about sex and nudity in general. I have seen many responses about this factor in the US that have nothing to do with disordered eating, poor body image, and the like, and it is these responses to which I am reacting. In your case, I can only urge you that if the shoe doesn't fit, please don't wear it! This wasn't intended as an attack on you in any way. :)