First of all, kudos to you for the radical changes you are making in your life - you have really attended to the physical aspects with much reward! I don't know how much you've done on the mental - they are tied VERY closely together - but still independent of each other.
ANd kudos also to you for asking this question - because part of you apparently senses there's the potential for trouble here, and I'd echo that, cause I can get a sense of that potentialy myself, just from your post! You're brewing under there, anticipating what's coming, and ready to start shouting "DON"T YOU SCREW WITH MY CHOICES!" Okay, I exaggerate. But you have asked a good question and you were wise to ask it.
A few things to remember that will help perhaps:
there is no right or wrong, there just IS. "Right" and "wrong" are relative and are individual interpretations of any given thing.
quite frequently in this day and age, the cosmic awareness of the child has overtaken that of the parents. It is quite difficult to see down a road one has not been down, and it is impossible to see down a road when one believes there IS no more road.
It's not a personal thing, their words, but it can often feel like it is.....and "help" to one, can feel very much like "criticism" to another (again, what is IS and everything else is relative and subject to personal interpretation)
How they respond to your choices is about them. How YOU respond to their responses is about YOU. You can't change them, convince them, or shut them up. You can only CHOOSE how YOU respond to what is taking place!
Pointing out the vegetarian dishes, especially when they have no idea what they're talking about, is quite likely annoying. But to them, it's most likely - and consciously - their way of supporting your choice and UNconsciously, perhaps easing their guilt for choosing a restaurant that isn't in line with your food habits.
Likewise the "getting all your nutrients" comment, which is also kind of a sublte, modified "CHANGE BACK" statement. They are doing what they understand. YOU are not (in their opinion). If they see YOU benefitting from your changes and choices, and these are choices they don't want to make, well then - they have something to deal with....or not, right? Thus comes rationalization, defense mechanisms, arguments, etc.
So, having said all that, my suggestion to you is twofold:
remember those things in order to assist yourself in ACTING through choice, rather than REacting through personal defense and perhaps, childhood and family patterns
go about doing what you do, but resist the urge to tell everyone about it. (I'm doing some suppositioning here) - you might want to share the glory, share the knowledge, share the wealth - or even actually want validation. YOu won't get it. As YOU see their pointing out the vegan dishes as annoying and THEY see it as helpful, YOUR talking about your new lifestyle maybe "helpful" under your label, but it's "ANNOYING" and in their face, to them. There's usually a secondary agenda going on. Be aware of what it is, whether it's YOU or THEM.
Stock up on what you need to stock up on and do what you need to do to take care of yourself. Bring stuff with you, eat before you go, whatever. Just do it quietly and sweetly.
They may or may not be able to let you be who you are, but you can certainly let them be who THEY are. I'm assuming everyone wants a "nice family visit" and keeping the topic off the table (so to speak) or choosing not to respond and debate it, will assist in that goal.
That's the end of my long-winded post in answer to your request!
Have a great trip and blessings-