AIBU to feel upset and insulted? What should I have said?

Dreadful behaviour from a socially inept fool, I am so sorry OP.
I have put on weight over the years because of my much more minor medical conditions than yours and honestly you have my total sympathy.
I hope all these positive responses out weigh the words of one stupid and no doubt ragingly unsuccessful man.

I meant that in response you could have said you had grown up, because he sounds extremely limited.

So sorry OP, what a horrible man. I'm so glad your DH supported you. I think a lot of people would have been lost for words in the moment.

Either ‘I can lose the weight but there’s nothing you can do about that face.’

Or ‘Imagine saying that out loud, how embarrassing.’

Some people have no manners. Your husband’s friend is one of them. I think you did the right thing - distanced yourself.

Im so sorry, that was such a nasty thing to say. What a prick.

Bloody hell. I can’t believe that people in their 40s would behave like this. Where on earth did your husband find such a scumbag friend.

A curt oh fuck off you idiot!!
If someone spoke to my DW like that
He'd be getting a knock on his door before breakfast and put in the picture in private.

Yes, the old ‘you’re looking well’ double edged sword. I find it amusing to bounce it back to them “Thanks, so are you!” as their reaction reveals their intention behind it. If they mean you’re fat they look insulted, if they don’t, they’re either happy or they say they’ve not been feeling well and self-deprecate etc. usually it’s the former in my experience - they’re often surprised - which isn’t a good look and clearly wasn’t meant to be complimentary

I read it as that that would've been a good response when asked what you'd "done to yourself"

So they knew you and treated you OK when you were size 16-18 but not that you're a size 22-24?

Size 18 is still quite large, I mean no judgement by this at all but they treated you OK but now you've gone to large to larger there's an issue?

I'd understand there would be a clear, unequivocal case of them being nasty if you were a size 8 when you last saw them.

I don't get this to be honest.

What a rude and horrible man! As a bit of a feminist who has always hated being judged by appearances, it always enrages me that it’s seen as a crime for women to age, whereas men don’t seem to get that vitriol. And very often in my experience the men making such awful unnecessary comments are ageing pretty badly themselves with no room to say anything! I’m glad your husband backed you - his mate, well it says a lot more about him than it does you.

Don't get what?

It's hard to say this without sounding judgemental but I genuinely am trying to be neutral.

What I mean is that at a size 18 the OP would have been quite a large person.

I say this not to be unpleasant just to be honest-size 18 is a large dress size. It's me being factual rather than being a judgemental person.
I don't personally care how big other women are.

Yet these men were friendly enough to her then.
Now she's gone up a couple, not several but a couple, of dress sizes again to a size 22 and all the sudden they're being awful.

Would they just not think 'Oh she's even bigger now.' but treated her the same?

It's not as if she's leapt from a size 8 to a size 22 which would be a surprise to them.
Again I do not say this to be judgemental, a leap from a size 8 to 22 would be a dramatic change. There's no denying it.

The answer to that question is “I’ve developed chronic illness that requires carefully balanced steroid medication. One day, this might be you too.”

"Fuck off" would have been my less polite response.
Why on earth anyone would think it appropriate to say this to you is actually beyond me, he's a cunt.