I had major issues with this as well. I never wanted to tell anyone that I was trying to lose weight, because to me that was admitting to a problem I tried hard to pretend I didn't have. I tried many times in the past to diet, and each effort would last a week or two, and then I'd fall back into old habits. That only reinforced my belief that I didn't want anyone to know I was trying to lose weight, because then they would also know when I failed. I was also afraid of my mother telling everyone who would lend her an ear that I was trying to lose; she was never really good at discerning what was appropriate for her to tell the neighbours and what wasn't.
Eventually they figured it out on their own despite my best efforts to not let them see my new eating habits and exercise routine. And for the most part they did exactly what I didn't want them to do, which was draw attention to it at every opportunity. My mother was particularly bad for this, and I'm sure my entire extended family plus most of the province of Newfoundland knows how much weight I've lost.
I've gotten better about talking to people about it, because it immediately becomes the topic of conversation whenever I see someone that I haven't talked to in a few weeks. People are also starting to look to me for advice about their own efforts, so it's difficult to avoid talking about it. People don't like hearing that I don't have any special magic pill though
So, don't worry, I was extremely secretive too, but I think it gets easier as time goes on.