Hi,
Like others said, some fish keepers fast their fish weekly, such as on Sunday. But I only have done it if they showed signs of SBD--then after a day of fasting, I fed peas--sometimes constipated goldfish will flip over. It is not really SBD but has the same symptoms so fasting will cure it.
I feed mine everyday too, usually twice a day, sometimes only once. It is best not to overfeed even though goldies beg for food--that is a natural thing for them--to beg and act starved.