They were a) filling up for the big journey and b) had the stomachs of hobbits, not full grown men. I think hobbit bellies are a little bigger than any full grown man's.
Plus, the book states nothing about one bite being able to fill people up. It says, and I quote:
Quote:
|
One will keep a traveller on his feet through a day of long labour.
|
__________________
"What mortal feels not awe/Nor trembles at our name,
Hearing our fate-appointed power sublime/Fixed by the eternal law.
For old our office, and our fame,"
-Aeschylus, Song of the Furies
|