Let's not make a big deal here.
I don't care whether or not if my FO is fasting, just had a good lay, sent the wrong mistress text message to his wife, or just lost his entire fortune after picking up some great investment advice from another fellow EK pilot.
I ONLY, and ONLY assess my FO gradually, from reporting till we shut down our last engine, on whether or not he's backing me up competently as a professional pilot.
I do not make a big deal if someone has misjudged his body condition and kept fasting while showing signs of fatigue or lethargy during Ramadan. I'll advise him to consider freshening up and so far, I only had to bring it up once, and taken positively since he knew he could make it up later in his total fasting duration, once he's off flying duties.
I will however, make a big deal, if someone turns up for work with heavy hangover, appeared severely lack of sleep with red eyes, and try to make friendly chats to get away with such irresponsible act.
My point is, it really makes no difference whether or not it's Ramadan. I will assess my crew the same way I do, every single duty day that I'm paid to do so to ensure safest possible outcome of my flight, without preconceptions.