Don't know if this will help any but being a guy maybe it will.

It isn't that these guys are trying to offend you, every potential relationship whether they end at first impressions or turn into long term commitment based ones, start with physical attraction right? Guys are very visual creatures, it's in our nature.

We all have our own reasons for being fit but no one other then us can know until they ask and how will they ever find out if they don't approach you, which is generally a flirtful scenario.

I could see a reason to be offended if the guys hitting on you are friends that suddenly changed their opinion of you because of the weight loss but if they're strangers they can't be blamed for being attracted to a pretty girl. And you never know who you'll pass up if you predispose every guy that approaches you as a superficial jerk.