This may come across as brusque to those with an overly active conscience, but I live my live by the following mantra: I owe nothing to no one.
I am not an open book and I owe no one any particular thing, not even the unadulterated truth.
Some queries are a bit intrusive. If some random stranger asked about your favorite sex position (missionary, doggy style, etc), would you divulge? If a convicted rapist who arrived home after serving the past 10 years in prison asked for your address, would you divulge? After all, the truth shall set you free! (sarcasm intended)...
In essence, my weight loss surgery is no one's business. If not divulging is considered a lie, then call me a liar. After all, it is one lie that has caused me to feel at peace for the past 2.5 years.