If you manage to drop enough fat off your frame (like how I lost 0.2 pounds last week, bringing me to an even 179.0), you will start hearing compliments.
Like for example, "Wow! You've lost SO MUCH WEIGHT!"
"Your waistline is SO SMALL!"
and my personal favorite
"You're just SHRINKING!"
All of which are, on one level, really nice to hear. And I'm not meaning to sound ungrateful with any of what follows.
However, if you've been fat for any length of time, you know that there's a tendency to be suspicious of compliments. Because usually the compliments you get as a fat person are, well, shall we say, "diplomatic".
"You look so GREAT today!"
"You're so fashionable!"
and the classic
"You have SUCH a pretty face!"
So we do have a tendency to be suspicious of compliments in general, no matter how genuine and well-meaning.
There's also, with the first set of compliments, the unspoken implication that you look SO MUCH BETTER than you used to! Which isn't really a compliment to your Formerly Fat but Fine Self, now is it?
So if you compliment a Formerly Fat Friend, and she doesn't respond with the enthusiasm and gratitude you think she should have, cut her some slack. It's probably nothing personal.
Maybe she's just not quite ready to hear it yet.