Those guys are right. It's your private business and you can keep it to yourself. For me, I just wanted to be transparent and stop my rapid weight loss from turning into my 'dirty little secret' ongoing. I've been amazed how almost all of the people at work are supportive. Others have not said anything, so I don't know what their opinions are but frankly, I don't care!
There is no shame in what I've done. I've had a heath issue that I have battled with for years and I'm tackling it head on.
That's the way I dealt with it and it worked for me. But the guys are also right, you are entitled to your privacy.
Good luck,
Deano