Everyone on the Enterprise can breath the same air and eaet the same food.

And if something is poison to even just a few of your crew, you forbid it and tell everyone else to eat almonds instead of peanuts. :nerdingout:

A lot of things were "forbidden" by social pressures. Alcohol was freely available (or maybe a simple security override, I can't remember) but no one drank real alcohol.

Note that they often invited aliens of unknown origin onto their ship (dignitaries, ambassadors, first contact, etc). This is hardly enforceable.