Nope there is nothing.
And food preparation next to toilets is pretty much banned in every first world country to boot.
The provision of food is a contractual agreement with the pax.
There is company rules for the prep and hold over times but these are more for liability reasons and the fact its very expensive to divert a plane with a full load having the squits.
There are regulations for some food types and it varies between country's (think pork)
There are also some food types which company's forbid for various reasons with excuses which may or may not have anything to do with the real reason.
For example peanuts are banned a lot of the time using the excuse that people can get a reaction from them. In reality its mainly because they make such a bloody mess. None of the other products on board are nut free.