This is a post I made to alt.polyamory in response to someone's asking "is there some way for me to help these women believe that they are beautiful just the way they are?"
("these women" = "overweight" friends who believe they are fat and ugly. The writer says "'fluffy' women are beautiful! Women are supposed to be soft." Note, I'm repeating these exact words of the writer because I address these specific words in my post. I am not repeating them to invite scoffing at them.)
Your best bet on helping them is to ask _them_ how you might help them.
But here's how I personally like to be helped about that issue. Note that I am a size-acceptance activist, so what I like is probably different from what some people who aren't size-acceptance activists like.
Don't call me or other fat/fluffy people overweight - that assumes there is an ideal weight. It's incorrect that there is an ideal weight - healthy people weigh all sorts of different numbers, and most people can be healthy within a range of weights.
On the other hand, if I say that I am too fat / overweight / what have you, don't immediately disagree with me. That's ignoring my feelings and implying that your opinion is more important than mine. I'm not saying that you have to actively agree with me either - just don't immediately say "You are not." You might say "I'm sorry you are feeling that way" or "How come you are feeling that way right now?" Or you might just squeeze my hand in sympathy - this is what my primary often does.
(Remember, your friends might not like this approach - I'm just telling you what works for me.)
Exception to this: If I say I'm ugly, then although I'm not usually fishing for a compliment, it's OK for you to say "I'm sorry you're feeling ugly. For what it's worth, _I_ don't think you're ugly, I think you're [whatever you think - beautiful, attractive, just right]."
The reason this is an exception for me is that I believe a person's aesthetic opinion is zir own and people's aesthetic opinions can differ. In other words, if I think I'm ugly, and you think I'm attractive, that doesn't discount my opinion. (I prefer my opinion is acknowledged though, not just disagreed with.)
Personally, I enjoy hearing people say that they find "fluffy" women beautiful. But I definitely don't like hearing it said in a way that puts down other women or implies that all women "should" have a certain kind of body.
(Aside on "fluffy" - a number of people don't like the term. I don't mind it personally, but I think it's kind of silly and nondescriptive. If you touch me your hand doesn't sink in like it sinks into whipped cream, and I'm not full of polyester fiber. I'm just fat).
So I would bristle at being told "Women are supposed to be soft." That sort of statement makes me feel like the speaker believes women exist mainly for zir aesthetic pleasure and that women who don't meet zir personal standards are offensive somehow. (The speaker may well not believe that at all, I know, but that's still what goes through my mind.)
I also don't want someone to try hard to make me feel or believe things that are contrary to what I actually feel or believe. If they disagree with me about a matter of aesthetic preference, I want them to state their disagreement as a personal matter, not as a universal truth. That feels more respectful to me. In other words, if I said "I feel too fat" and you wanted to disagree, I'd like you to convey something along the lines of "I hear you saying that you feel too fat, and I'm sorry that you feel that way because I think it must be painful. I'm only one person but my personal opinion is that I think you're attractive as you are." (That sounds very stilted, so I wouldn't necessarily want it said exactly like that, but I like those sorts of things to be conveyed.)
Something else I like from people who care about my appearance issues: I like them to learn about unreasonable appearance standards in my culture. I like them to understand that these standards create personal body hatred in almost all women, fat, thin, and in between. I like them to understand that for almost all women, struggling with this personal body hatred takes up a lot of time and energy whether we want it to or not, and that such struggles aren't the result of a silly personal neurosis, they are due to overwhelming societal pressure.
Personally, because part of my struggle against personal body hatred is to focus on aspects of myself other than appearance, I also like to know that people who care about me appreciate me for qualities that aren't related to what my body looks or feels like. It's wonderful to be told I'm beautiful, but it's also important to me that people who care about me let me know they think I'm smart, thoughtful, interesting, creative, or whatever other positive traits they notice in me.