My girlfriend is in the process of losing weight, and the topic comes up between us occasionally (at her instigation), usually with a context of "I'm going to be so much hotter in a few months".
She's very much doing it for herself, and I don't think there's unhealthy body image stuff attached. From a purely objective standpoint, I can acknowledge that there is room for her to get slimmer without being unhealthy. I, however, being thoroughly enamoured with her, think she's the hottest thing on two legs irrespective of what size dress she wears. I generally express this opinion, but I'm a little worried that it might come across as rubbishing something that she's doing for herself.
I don't want to express either "you shouldn't lose weight" or "you'd be hotter if you did lose weight" - I think she's gorgeous, and I think she'll still be gorgeous if she lost some weight. It makes no difference to me, and it's her body anyway, I have no say in the matter even if I did have an opinion. How do I respond when she brings up the topic, so that it doesn't come across like I'm either being unsupportive of her efforts or telling her she needs to lose weight?