For babies who drink formula, this usually does not present a problem, as they are usually on a schedule.
But for babies who nurse (I am happy to report that the number of nursing moms is on the rise), this presents a bit of a problem. My wife likes to call herself "Mommy's 24-hour open bar," so I understand very well how nursing moms like to provide when baby asks. And this is a wonderful thing. One might argue that the only downside of nursing is that babies love it! and don't want to give mommy a break.
Before a bris, however, the problem is twofold.
A: Nursing during the bris is impossible - for obvious reasons.
B: The baby's system needs to be cleaned out in anticipation of the bris.
I assume I don't have to explain the first reason, so here is the explanation for reason "B."
The baby will be crying in a way he might not be consolable while the bris or bandage change is taking place, and if he happens to have recent food in his system, there is a good chance he'll spit it up. "Spitting up baby + crying and can't be moved due to position he is in when caring for his circumcision wound" is not an equation we want to deal with.
After the bris he can eat all he wants.
But it is not worth risking a spit up during the bris or when I am checking his bandage right after the bris. Choking baby is much worse than crying baby.
I hope you will agree.