Thank her for the gracious invitation and ask her for the menu ahead of time. You could say you have some food intolerences (don't be specific) and once you see the menu you might ask if you can bring an extra dish to share with others? People are much more sympathetic to food intolerences than they are of "diets". Don't know why, but that's been my experience.
Have fun at the party ~!!..
Offer to bring a big salad! I'm sure she'll appreciate it. Then during dinner, you can fill your plate with mostly salad, which will mask the fact that you aren't eating the other stuff (unless of course there ends up being something served that you can eat!) You can always put a tiny smidge of other stuff on your plate, and pretend that you are eating it too, if you are self-conscious about it!.
I either bring my own food and explain that I am trying to lose weight or I would ask what the meal is ahead of time and see if I can pick things that are on plan. I've found that most people understand the struggles of wanting to lose weight and are accepting of my situation. I've stopped thinking that I am going to hurt someone's feelings because I won't eat their food. I wouldn't do that to anyone, so I hope that no one would do that to me. I've also found that when people do make a big deal about me not eating whatever "off plan" food that they are eating it's because they may feel guilty about their own indulgence. A lot of people have been really interested in what I'm doing, so it's been nice to talk to others about my struggles and how this is helping.
I know it's hard in new situations. I hope that you have a wonderful time at the party! I know how hard it is to make new friends (I've been at home for 5 years now with my kids)...
If the hostess is someone I want to have as a real friend, I would be honest. I'd address it ahead of time, saying something like "I have life-threatening struggles with obesity, and I'm on a very restricted diet for my health. Would it be all right with you if I brought a salad to share for dinner?" If she's someone I don't think I really want to know well but find socially useful, I'd go with "I have some food intolerances. Would it be all right with you if I brought a salad to share for dinner?"..
I really like the salad idea! Thank you. I will do that!..
I'd just tell her I'm on Medifast. Women bond over diets; it could be the makings of a nice friendship. No reason to make a big deal over it; just be matter of fact about it and nobody will make it a big deal...
I would say bring a salad or some yummy roasted veggies, every host loves something extra and then you can make sure you are eating some thing you are able to- if needed you can make up the protein later..
I agree with what Gigi said - diets are usually something women friends talk about. It seems everyone has either been on a diet or loved/known someone who has. It's like getting a group of moms together it is inevitable that the conversation will eventually move into labor stories. Don't be afraid to mention it to her quietly..
Plus, Lyn, you've lost an incredibly impressive amount of weight. No reason to hide that with people you want as friends. Let her know how long you've been doing this and that you would love to bring a salad or roasted veggies to share, especially if you have a special something you've been making while OP. This could become a really great topic of bonding conversation, ya know..
And if she or the others give you grief about Medifast, diet, weight-loss, etc., well, better to know at the beginning of the friendship...