In my experience the fasting FO's I fly with don't break the fast because they are travelling. That is because they don't want to make up for it at the end of Ramadan whilst their mates are partying hard during Eid. So that tells me they put their social life ahead of my safety and of the rest of the crew and pax. Oh but no it doesn't! He is fasting for Allah and therefor if anything goes wrong it it Allah's will, nothing we could do about it anyway. A flight deck where rational thought and commonsense are necessities is not compatible with a fatalistic mindset, not matter what the source.
Airmann, to answer your original question, companies might have a policy, but how do they know who fasts and who doesn't? Thank you for forwarding your gods post to pprune, that might be a first but I suggest you are on the wrong forum.
Now back to my spaghetti and Pirate movies before the Mod wakes up....