Hi,
I kept it secret apart from my direct family and one person at work who I needed to cover for me, (my job involved quite a bit of meals and events and it was around Christmas). I was a bit worried about how people would react or 'judge' me and felt that I needed to get comfortable with it myself first. I only really started telling people about 2 or 3 months after when I found that people were asking about the weight-loss and were actually getting discouraged because they were dieting and going to the gym and were not getting the results that I seemed to be getting by doing the same thing. I was massively surprised by peoples reactions and feel guilty apart underestimating them. I can honestly say I have never had one negative comment, to my face at least. Mostly people have been so supportive, and at the end of the day, its what you think that counts. Do whatever you feel comfortable with, and hope it all goes well!