"Your metabolic rate is twice normal. This means that you are much less resistant to http://fallout.wikia.com/wiki/Radiation and http://fallout.wikia.com/wiki/Poison, but your body heals faster."

This is the description of the trait in the original fallout ( and 2). But the effect is contradictory to the real life, because radiation in real life has a negative effect on your metabolism. Your metabolic rate wil slow down a bit. So that wouldn't be a very big problem for people with a high metabolism, but much more for people who already have slow metabolism.

As a result a fast metabolism should grant an advantage against radation.

I'm going to do a 'Rad Child' playthrough on NV so I wanted to take the perk version of it, until I saw the effects of the trait version in Fallout 1 and 2. I'm going to take it anyways because I'll follow my common sense.

Technically the lower resistance to poison is not realistic either, because people with higher metabolism will get rid of the poison much faster than someone with slower one.

Really, it should give increased resistances to these things, higher health regen at the cost of requiring more food and water for survival, because you use it up faster.

But it's a video game, not everything's got to be logical and realistic.

Exactly.

Well from fallout I expect things to have a logical explanation. Though not per se realistic in practice.