Oh me too

Sometimes people will say something negative about themselves because they're hoping you will say something positive, instead. I used to do the same thing. Whenever I was feeling insecure about my looks or weight, I would say something negative about myself, because my husband would tell me it wasn't true and would give me compliments that would boost my self-confidence. I don't do that anymore, because it's not a very healthy way to be confident in yourself, but it certainly was effective. Do you think maybe your girlfriend is just feeling insecure about herself? I would talk to her about that to see if maybe it's something she'd like to work on in herself. You can also try to give her honest compliments on a regular basis. It's hard for a girl (or guy!) to feel unattractive if her loved one is telling her twice a day that her shirt looks good on her, or he loves her laugh, or he thinks she's pretty.

Other than saying things like, you dont look fat to me, i would love you even if you were the size of a whale, etc.

One thing that i find is pretty useful for all people to remember:

When you see other people who are overweight or a but chunky, etc. Do you judge them for it? Do you focus on it and think "whoah look at fatty over there!"?

I don't. Sure, i notice when someone is fat, but only as much asbi notice someone whonis really thin or just a normal weight. It doesn't change how i interact with them or if i would be their friend, etc.

Other people aren't judging you if you are fat. (Im sure there are some, but they are terrible people, and their opinions dont matter)

Most people are too concerned with how they look to notice/care about how you look. So dont worry about it. Just aim to be healthy. Dont stress over weight for looks.

"Fuck I love your curves"

Or ask if they want a back rub. Gets you out of alot.

"More cushion for the pushin'"

and

"I like 'em real thick and juicy"

have worked well for me.

"You sure are, P H A T! Pretty Hot and Tempting! "

"You are not fat, you are delicious"

Then give her some love bites!

Here in the US there is always going to be messaging telling women they need to be underweight. Having had a friend who died while anoexic and underweight (I can't be sure of the causal relationship but I'm sure malnutrition was a factor) the danger of body dysmorphia is, to me, very real.

I'd say someone's negotiation with their own body is up to themselves and their doctor, but even primary care providers in the US are freaky about weight. Are you a fat lycanthrope with cancer? Statistically your doctor is most likely to fixate on your extra girth.

As someone's girlfriend myself, I'd say acknowledge both her weight gain and the fact that she's not technically overweight (I'm assuming this based on you saying she is "not fat at all", but you can look up some local statistics in your country to see for sure). To me, it would completely mess up my ability to gauge my own size if I were lied to about having gained weight. (This has happened to me and it makes it confusing to buy clothes because I have absolutely no idea what size to try on. Pants look like they'll fit fine and then they're completely wrong in the fitting room.) So tell her that yes, she has gained weight (and that's okay).

One approach to weight gain, if she really has gotten significantly bigger, is that people can be simultaneously fat and beautiful. I won't go into detail, but you can look things up. There's a world of beautiful fat ladies out there.

Another approach is to recognize that society often tells women they have to be beautiful

but that's not true! Your girlfriend isn't here to look pretty; she's here, like everyone else on this planet, to have some fun in life. So my perspective on it is that I'm not beautiful, and that's fine because I'm not here to be easy on the eyes, I'm here to play video games and go swing dancing and learn new recipes. Similarly, my body's purpose is not to appear beautiful; my body's purpose is to carry me through day-to-day things, like dancing and eating good food and moving into a new apartment. To that end, I go to the gym just to be strong enough to do what I want to do (like lift boxes into my new apartment), not so I can look good for some other person's opinion.

It might not go over well if you were to tell her this right now when she's sensitive to it ("Hey babe, yeah, you're fat and ugly, but hey, you're ugly despite being fat, not because of it! They're two separate things! And also, it's okay you're ugly! You're clearly not here to be pretty!"). But this is a mindset that has very much helped me personally over many years, and maybe you can introduce it slowly to her and explain it in a way she will understand. You know her better than any internet stranger.

"okay"

Phat like 1994!

That depends heavily on who she is, and what your relationship looks like; a lighthearted response might work best for one person, while launching into a serious discussion about body image might be best for another.

My go-to response when my wife says something bad about her body is to just respond with "You're beautiful." and leave it at that. Sometimes I throw in a "Hey, don't talk about my wife like that!" for good measure.

"No you aren't"

"no, you're thicc"... then explain to her it's the most popular body type by today's beauty standards... which fluctuates and health and happiness are all that matters... and youd love her if she was a brain in a jar, but she happens to be really hot... something like that
also, get an Australian Cattle Dog... that'll force ya'll to be more active...

well, just get fatter yourself

I'd say nothing, it's a statement. Doesn't require any response from me.