In my part of the US, a lot of our "old" houses were built before indoor plumbing.

So when the plumbing was installed, obviously some went to the kitchen. And the bathroom, which previously didn't exist, was often an addition to (or a division from) the kitchen -- with a doorway [with a door] betwixt the kitchen and the bathroom -- because that made the plumbing easier.

IIRC, that particular feature disqualifies the home for financing with both the VA and with HUD for reasons of hygiene.

So by extension: According to VA and HUD, hygiene requires at least one door and at least one additional room of separation between the place where you shit and the place where you eat.