Complex sentence: Several orders of monks in medieval Europe restricted or banned the consumption of meat for ascetic reasons, but none of them abstained from the consumption of fish; these monks were not vegetarians, but some were pescetarians.
Split into simpler sentences: Several orders of monks in medieval Europe restricted or banned the consumption of meat for ascetic reasons, but none of them abstained from consumption of fish. So these monks were not vegetarians, but some of them were pescetarians.