From the Online Etymology Dictionary:
fast (adj.) - O.E. fæst "firmly fixed, steadfast," probably from P.Gmc. *fastuz. The adv. meaning "quickly, swiftly" is also in O.E., developing through a sense of "firmly, strongly, vigorously," or perhaps from the notion of a runner who "sticks" close to whatever he is chasing. The sense of "living an unrestrained life" (usually of women) is from 1746; fast and loose (1557) was an old cheating game; fast food is first attested 1951.
fast (v.) - O.E. fæstan "to fast" (as a religious duty), originally "hold firmly," sense evolution is via "firm control of oneself, holding to observance."
-Tim
