Should I bend my dietary rules when meeting my significant other's family?

I wouldn't - I can understand wanting to make a good impression, but you have to be yourself, and how you eat and why you eat that way, are a part of who you are. Let them get to know the REAL you.  Plus, it may cause issues down the line. If you bend now, they might expect you to bend later. "Why won't your partner eat this? They ate something like it last visit?!" I've also noticed that some people don't respect your choices as much if you cave.