First of all let me just say that Stewie rocks!!! He's my favorite
Secondly, they'll get over it.
My mom didn't get mad at me or got offended or anything because I didn't eat her food, BUT she nagged and nagged and nagged about Atkins. Then she saw that my health improved and she saw my weightloss. By the time December rolled around she was doing Atkins with me!
Most people will come around and they'll begin to understand why you choose to not eat those things, etc. It just takes time and there isn't really much you can do about the whole situation. They have to be understanding and that's not something you can control.