Well, in my experience, even if you are not someone who is gaining or losing weight or appearing to be sick, gossipers will find something to gossip about in regards to other people. So, it really doesn't matter, as everyone gets talked about no matter what.
Dealing with weight gain and medicine side effects, and people who stare.
I don't care who knows that I am sick. In fact, when I am fat from prednisone, I make sure every time I end up in a room with other co-workers and they talk to me, I say something along the lines of "Owww....my face hurts so much....this medicine I'm on makes you swell really bad and I'm so swollen it's smooshing my face. Sorry, it hurts to talk". Anybody who would make fun of you to other people will promptly be scolded by everyone else, as it is extremely low to make fun of someone's appearance when it's caused by medicine smooshing their face! Now I know if people stare it's because they're wondering if I'm ok and not wondering why I "look funny" which is much easier to deal with.
Telling people I don't feel good.
If people ask how I am doing, I tell them I am really sick, or I tell them I am really tired, when I feel that way. If they look like they feel bad for asking I tell them it's not their fault that I am sick or tired, and that there is no cure for my disease so it's something I'm sorta used to, I am ok with talking about it and I just hope they understand that I won't feel too good pretty often. They seem to take it pretty well, and for the most part now I get "Hey, you hangin in there?" or "Hey, you look like you feel pretty good today!" depending on how I look health-wise. Much easier knowing people understand what's going on with my health.
Answering the "So what does that disease do?" question.
I tell them my immune system is defective and instead of attacking germs, it attacks my organs in my digestive system. My stomach, my intestines, just about everything. I tell them when the immune system is attacking, the organs get sick and don't quite work as well, so I get really sick and tired from not being able to eat or digest properly. I tell them it's like having the flu and food poisoning at the same time, and almost always get "OH I get it, wow that's not fun" as the response. If people still don't get it I just say "it makes you have to go to the bathroom about 10 times a day, which makes you really tired and malnourished" and leave it at that.
Dealing with stupid medical comments.
Sometimes when they ask me more about the disease, people give stupid medical advice like "maybe they can give you some medicine" when I just told them I have to take a lot of pills for my disease every day, or my favorite "you should see a specialist" right after I tell them I've seen specialists and there is no cure from any doctor in the world. I get annoyed but understand that most people can't wrap their minds around the "incurable" part and they are suggesting things without understanding that it doesn't work. I figure since most people will only come down with colds, flus and maybe an infection or two, they have no idea how doctors and hospitals work when you have a more serious health problem.
Having people understand you aren't a freak of nature.
Inquisitive or talkative people usually want to know how come I got sick. I tell them that there are actually lots of disorders caused by the immune system attacking yourself, and that immune disorders are about as common as cancer, i.e. all you need is to be in that unlucky 1% and you end up with a lot of medical challenges to face. Most people usually comment "Wow, I can't believe they make fun of people who have to go to the bathroom a lot then, if that's all it takes to get it." and I say "That's the other reason you don't hear about it often, jerks in TV and movies who make fun of this disease make most of us feel embarassed". The more people who understand that anyone can get crohn's and that it's not disgusting or funny or weird because it's not our fault, the better!
Overall, I have found that talking to people, trying to give them a basic idea of this disease and autoimmune problems in general, helps them be more understanding and sympathetic to others with any health problems. It also saves me a lot of stress that would otherwise be caused by stares, rumors, jokes, and misunderstandings.