First Day-good excuse?

I am into the first few hours of my first day. I mentioned that I may be doing this to my boyfriend and he pretty much thought I was being silly. Not even going to tell anyone else. The problem is I'm expected once a week to see my parents. If I don't eat when I'm there, they are going to ask questions. If I tell them what I'm doing they won't understand, and I'll get the "you have an eating disorder" speech. I just need a good excuse so I don't have to see them this week.