I have lost weight a couple of times, gone down to 105-110 pounds. So, not in a WLS context, but a general one, I can address this lol.
1. how much weight did you lose? this one is just intrusive as hell. if the person is just socially inept, my response has tended to be along the lines of just as much as i needed to feel healthy. most people don't inquire further. if the person is bitchy or gets pushy, i tell them they're being intrusive, and that works fine. they offer a pseudo-apology, and move on. *shrugs*
2. lol @ you look so good..i didn't recognize you
again, this one can either come from a bitchy place or just a socially clueless one, and i would respond accordingly. i've gotten that a lot but minus the "you look so good part". that's just ridiculous. i, personally, just say..you look great. and make no reference to the past or to recognition difficulties, when a person has lost a lot of weight.
3. aren't you done yet?
i got this a lot. i even had a couple of people ask me if i had been hospitalized recently, which is preposterous lol, because i definitely looked and felt healthy. to this one, i've just said, i am doing just fine, thanks for your concern lol.
4. you should have done this years ago-
this one is just disrespectful and condescending as hell, no matter how you look at it. nobody has ever said this to me. my response would've been..you should've stopped being an ass years ago.
5. good for you..i hope you'll keep it up.
this sounds pretty snarky but could come from a socially inept person who means well lol. i would just thank them for their well wishes. if the person is being a snide, they'll hate it because it's disappointing to them when their snark doesn't have the intended effect.
if the person is just clueless, then lol.
6. you look amazing--what's your secret
hmm i don't there's anything wrong with this. i mean the secret part is hokey, because it really is no "secret" that it takes a lot of effort, discipline, consistency etc. to workout regularly and eat well, and for those of us with metabolic issues that just aren't fixable without an invasive procedure, it takes surgical intervention followed up with mindful eating etc as with everyone else. but, since i've only lost weight with exercise, dietary changes (low carb basically) in the past, i had an easy time telling people what kind of changes i had made. i would just say i've been low carbing, doing a mix of HIIT and weight/kettlebell training, or whatever else I had found useful at the time. this question doesn't bother me at all. i don't think it's snarky or rude, in the least. i, especially, had an easier time answering if another overweight person asked me this, because we could both empathize with each other.
now with wls, i don't think i want to publicize it too much at all, and only because my family is extremely judgmental and full of shit. it's only going to attract passive aggressive and disrespectful personal attacks every chance i cross paths with most of them. i think, barring my closest friends and partner obviously, everyone else is likely going to get the low carb and workouts answer. meh. i wish i could be "honest", but it just doesn't fit well in my life currently.