Fast Metabolism is a trait in Fallout, Fallout 2, Fallout Tactics and J.E. Sawyer's Fallout Role-Playing Game. In Van Buren, it was renamed to Increased Metabolism.
Fallout, Fallout 2, Fallout Tactics, Van BurenEdit
This trait adds +2 to your Healing Rate, but your radiation and poison resistances start at 0%. Unavailable to ghouls and robots (Fallout Tactics).
J.E. Sawyer's Fallout RPGEdit
Your metabolic rate is increased. This means that you are much less resistant to radiation and poison, but your body heals faster. -10% to radiation and poison resistance, +2 to healing rate.