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?
This subject is interesting. I'm going to assume your girlfriend's personality suggests that she isn't too sensitive about this stuff given the information.
Objectively, anyone who can healthily lose weight, should lose weight if the goal is overall health. (Even slight variations of weight have medically-proven effects on health and lifespan)
Please, do not ever tell anyone that they shouldn't lose weight, barring serious medical concerns (and never tell anyone, especially your girlfriend, that they should lose weight, either). **
Your viewpoint is healthy, so don't be ashamed of it. Embrace it. Personally, I think you have the right idea, you're just having trouble expressing it.
When she says:
I'm going to be so much hotter!
If you get any hotter I think I'll melt.
Something like this expresses your opinions of her currently, without telling her that she should or shouldn't continue.
You should also mention something positive to ensure that she knows how you feel. Something like:
It's awesome that you want to be healthier, but I'm proud of you either way, and [insert gushy comment about how pretty she currently is]
In fact, the less you mention weight, the better. If I were in this situation, I'd keep it in the context of health.
Non communication tips that might help:
** Clarification: Please do not mistake my suggestion on weight loss comments to come from a medical point of view. There are people who need to lose weight and there are people who need to gain weight. If the problem is immediately-life-or-serious-harm-threatening, it's okay to speak up. If not, I recommend leaving it to the doctors or go to medical school because otherwise it's not really your business.
I have a very similar situation in my relationship where my SO is trying to better themselves despite me thinking they're already perfect. My advice for you is to get excited and stay encouraging! When discussing this, focus on the benefits for her, not yourself--that's the reason she's doing this after all. For example, definitely don't say "you'd be hotter if you did lose weight" like you mention in your question, instead try to figure out what her goals are, and encourage her towards those goals.
For example, try asking if she has any goals (or if she doesn't, it could be fun to set some!). Is it fitting a certain size of jeans or a certain swimsuit? Or maybe it's a weight number. Once you know what she's working towards, you can specifically mention this when discussing her plans:
I'm excited to see you in those jeans, I know you'll make them in no time if you keep this up!
Or even compliment her on what you've seen her doing
I can't believe you already ran X miles this week—you're kicking butt!
Don't overthink this. If she's decided to do this, then she has her own reasons and as the SO, the best thing you can do is push her forward!
From my partner's own weight loss work, I can tell you precisely what you don't want her to focus on.
Don't let her want to lose weight. Don't even let her measure her weight, if you can help it.
Let me explain. The problem with weight is that it's a really bad estimate of how much fat you're carrying. Sure, if you're 5' tall and 200lbs, you can guarantee at least 50lbs needs to go. But day by day, and even week by week, you can't clearly see it change. You may be dehydrated and under weight. Especially for women, water retention during the period will cause it to go up again. Even how much you're going to the toilet will be an issue. If she's getting on the scales, she really doesn't want to do it more often than every week, and really every month is better.
And worse than that, muscle weighs more than fat. My partner was devastated when she came back from a week's diving holiday and found she was slightly heavier than when she left. She'd actually shed a load of fat and put on some muscle - but using weight as the measurement was a disaster, so much so that she stopped trying to get fitter and put on a stone of pure fat.
Instead of using weight, measure it in a way which matters. With my partner, we started with a belt, and we simply looked at losing notches on her waist size. Simple as that. But that directly relates to what she's looking for, which is dropping clothes sizes, and more than that, it's something which really doesn't vary too much.
If she's exercising, the other clear way to measure improvement is by achievements there. Run times, weights, reps - that's all measurable, and she'll see improvements creeping up there.
And don't let her join a diet club.
For starters, they're all based on weighing yourself. Like I said, that's nonsense.
For a second problem, I'm not aware of any which have criteria based on science. Slimming World and Weight Watchers are the two best-publicised ones in the UK. Neither has a shred of reasoning for their rules. They simply are not based on facts, science or evidence. Slimming World in particular with its bizarre rule about unlimited carbs is actively harmful to its victims.
And for a third problem, they encourage yo-yo dieting. As the "biggest loser", you're rewarded - never mind if it was unsustainable and you binge on ice cream and cookies next week. They simply aren't set up structurally to reward slow and sustained fat loss.
Instead, practise portion control. Avoid snacks. Eat fruit. Eat fresh veg. Do exercise. Unless you have a real medical condition (which is very rare), the fat loss and clothes size loss will happen naturally and in its own time. And better than that, it'll probably stay off too.
If you genuinely think you need advice on sorting out what you eat, talk to a dietitian. Unlike nutritionists (who don't need any qualifications, or whose so-called 'qualifications' are not necessarily based on medical fact), a dietitian is a healthcare professional. A consultation won't cost you more than a couple of months membership at a diet club, and it'll do you a lot more good.
I think she's gorgeous, and I think she'll still be gorgeous if she lost some weight. It makes no difference to me,
At the same time you state:
From a purely objective standpoint, I can acknowledge that there is room for her to get slimmer without being unhealthy.
Now I actually disagree that this implies "she's not doing it for me". That it does not change that she is first choice for you actually means that she is not trying to effect a change on your choice but rather on how happy she feels you can be about it.
So likely the right frame of mind is "I cannot imagine right now being more infatuated with you than I am but are certainly open to let myself be surprised".
And in some manners it can turn out like interior decoration: you cannot really imagine assigning any significance to it but when getting to live with its results, one has to acknowledge that it does actually make a difference.
So keep your mind open about being impressed and don't sabotage her efforts by closing your mind to the possibility of being appreciative of the results.
For me personally it's not as much the result of dieting (when starting from reasonable size that is) but of exercise that's most relevant: I like touching something feeling alive, and basic musculature does that job better than either fat or bones.
Again: nothing wrong by letting your tastes be led by who you chose to embrace anyway, but be open about appreciating changes even if they don't aim to change your choice.
Weight is a touchy subject. My partner and I have both varied our weight quite a bit over the past 10 years or so and over that time we have both been sensitive in our self image.
What I have learned is that it is much much better to focus on health than looks. Since you don't mind either way, you can emphasize that you like how she is now while still being supportive of her health. Even though weight and health are tied together (it's possible to be unhealthily over/under weight), it's also possible to be a healthy weight and have an unhealthy food lifestyle or an unhealthy relationship with food. The number on the scale is just a number.
It's so great that you're focusing on being healthy and I really appreciate that. The number on the scale doesn't matter so much to me as long as you are looking after yourself!
This, in addition to sufficient compliments/gushing on her current looks will give her support in the right direction and still allow you to compliment her all you like.