A clue is in the next line:
S[anctus] Liberalis Attinensis Episcopus, Heliodori discipulus…
Saint Liberalis of Altinum, the Bishop and a student of Heliodorus…
In other words, "Liberalis" is the name of a saint.
So I'd translate your sentence something like:
[Sanctus] Liberalis corporis & sanguinis Christi Domini alimenta sustentabatur.
[Saint] Liberalis was sustained by the nourishment of the body and blood of Christ the Lord.
According to the stories, Liberalis fasted extensively as a form of mortification (refusing to eat or drink except on Sundays); I assume that's what's being referenced here.