interesting Q, carrie. just what does his doc want your dad to eat? in general - as rosey said - it SHOULD be OK, but there are some surgeons out there who want their patients on two protein shakes and one meal for a month or so, and that may not be the best thing FOR YOU.
are you the cook in the house? are you and dad living together? does he cook for himself? see - the Q i'm wondering about is this: if he were living in, say, NEW JERSEY
without family nearby, could he manage the preop diet? and more important, could he manage the AFTERWARDS eating plan?
it's one thing to SUPPORT someone, to help them along, but it's quite another thing to take the responsibility of someone else's eating habits.