Could you tell your parents that you are doing a special "cleanse" and that you need to be on a specific diet for several days? That way, you can tell them you will just eat beforehand in order to not make them prepare anything special....
I too keep this a secret as to not be a "walking mc defender" 24 hours a day. I would rather them think I am wierd for not eating, than to think I am weird for doing the mc!