My mother, my grandmother+her husband, and my brother know. Those are the only people who I've told and that's it until I feel ready.
The reason why is that years ago I was ready to do the procedure. I did all my prerequisite testing (which was grueling for this particular doctor, guess he really wanted to make sure you were committed..), I had all the money in cash, save for $1000~ saved up, I was ready to schedule my date of surgery and everything. I made the mistake of not stopping my mom when she told a group of family members at a gathering about the decision. They berated me for it, told me I would die, scared the living crap out of me with horror stories (which I don't even know if they were real because they were anecdotes of anecdotes.. lol), and just talked me out of my decision.
It's been about 4 years since that and I've gotten worse, despite my efforts in the gym and my diet changes. I now know that I should have just pulled the trigger years ago when I was ready. Now instead of mourning the time I lost by mounting that pressure on myself with having that conversation with people, I'm just going to do it. Screw it.
You tell the people that you trust to accept your decision and help you through the drawbacks if you happen to cross that bridge later in life. I don't need the stress of others' opinions clouding my mind and hindering my progress. I'll tell them everything they want to know when I hit my goal.