Fast Metabolism is a Fallout, Fallout 2, Fallout Tactics and Lionheart trait. 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).
|The following is based on Lionheart and is not considered canon.|
You have an increased Healing Rate, but your disease and poison resistances start at -10%. Feralkins cannot take this trait.
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.