I am going through the same thing. Just waiting for a date!!
I have told my parents and sisters a few of my close friends who are always supportive, and my uncle, because he would be shocked if seemingly out of no where I didn't go to town on chinese buffets with him. I don't mind certain people knowing. I know some of my friends have already told other mutual friends/ their family, which is not ideal, but I don't see them so I don't really mind. I am mostly worried about people I see day to day and people I am not close with (like coworkers who I wouldn't talk about other personal things with) knowing. For me it is a personal life change, and I am only sharing it with people I think will be supportive and care about me, not just what I'm eating or look at me as a statistic for how it works. I don't need judgement or criticism (I do enough of that on my own).
I am trying to get single incision surgery, so that there aren't scars to be asked about. I liked the gallbladder surgery excuse. I have been debating whether I should make up some story about the surgery or pretend it didn't happen at all to those I am not telling. Do other people have excuses they have used for the scars or weird diet or rapid weight loss? I am very curious!