There are reasons why people talk about them being dieting. Some people just brag (especially in front of fat "friends"), some need more eyes to watch their eating habits and some just always try to get an extra attention.
But according to my experience no people with serious body/diet/ED issues talk about them publicly. I guess that's one of the reasons why the pro-ana community is so big&tight&sympathetic. Girls who are secretely starving value the virtual place where they can share their thoughts and take a good care for it, since there is no other for them.
The day, when I have stopped talking about my diet and all the other body related issues meant a big change in my life. I don't order low fat meal when being out for a family dinner anymore (instead I am always "too sick to go anywhere"), I don't search for little fitness tips and tricks online anymore (I am all about the big challenges now) and need no one to consult my actions with - I only need an inspiration and place to share.
Being "publicly dieting" and "secretly starving" have nothing in common. They are the opposites of each other.