I was the same at first. I didn't tell anyone at work except a couple of confidentes.
Once I'd lost alot though, I didn't care anymore. I think the fact it was working so well meant less negative comments and also the few negative comments that there were made no bit of difference to me as I knew it was working.
The thing is, peoples comments can only affect you if you let them. You can either restrict their knowlegde about your life so they can't comment or just ignore them and do things your way.
You could always just openly have your shake at work. No-one need know the programme that you are following or that it is total food replacement as there are two other meals a day and they wouldn't know you weren't eating unless you told them. You could easily explain that you are on a diet and taking a shake is easier than preparing a meal to take in everyday. You needn't name it, just say it's a protein replacement shake. For the first few months, I just made sure that the sachet was in my draw or face down and when Ipoured it into the shaker the writing faced away from everyone else. When I put the sachet in the bin I crumpled it up with the writing on the inside.
The way I looked at it, was that it was actually no-ones business except mine, and that extended especially to work colleagues. At work, I am still selective what I tell people especially when they ask how much I've lost. I just give a vague answer and end the conversation.
Alex