At my Catholic schools on saints days, there were quite a few, mass and communion were obligatory, these would be held at the beginning of the school day. Way back then one was expected to fast before communion so that meant no breakfast
We were allowed to bring sandwiches in and eat them at our desks afterwards. I do remember an occasional fainting (not me, I was built of sterner stuff )
. However, the fasting only lasted to mid morning. Not sure how diabetics would cope, possibly they would get a dispensation on medical grounds.