Sninge, I have recently been involved in commenting on some new guidelines for inpatient care for people with diabetes (pwd), here. Policy seems to be that PWD are offered the full menu, and whilst not encouraged to eat sugary foods, they make their own choices.
I breathed an inward sigh when I read that patients requiring GF diet could go to an a la carte option. Yes, I'm GF. I rarely look on that as being a big won, but I'll take it in this instance.
On a serious note, your challenge may be a round the confusion your suggest your father had on admission. Of course, confusion can be a sign of infection, dehydration or imbalanced electrolytes, as well a other worrying things.