I grew up thinking it was a PA Dutch phrase, as my great-grandparents came over from the Germany/Holland area and this was a favorite of theirs. I heard it often growing up in PA, usually in the context of "snacking" when one shouldn’t, such as before supper. "Stop fressing, you’ll not eat your supper."
CSD, you slay me man! "Do not feed this boy." I’m dyin’! Too funny. Why does that sound like a vintage TV or movie bit? Did this really happen or are you yankin’ me?
oneiron, as Yiddish is a dialect of German it is entirely understandable how two diverse cultures could use the same lingo. I too grew up with "fress" as a term for eating. My background is similar the The Dog’s; no Pennsylvania Dutch in my blood, just the occasional boiled brisket or gedempte chicken.