if you look carefully or ask questions in your company you may be surprised that there is indeed guidelines available to you.
I really do not think that a captain should have to go looking for such advice.
It should be proactively made clear by flt ops. If it ain't then, of course, refer to above by Catabolic IBS.
(just learnt a new word - wonder if our body builders know that anabolic can have catabolic effects - where least desired
)