Maintaining metabolism while working in the office?

I’m a programmer, and part of my daily “job” is I have to sit around for extended period of time. I read from somewhere (I think Shell gas station) that if you are physically idle for more than X hours / minutes, the metabolism shuts down. This obviously is not good for people trying to stay fit and/or trying to lose weight.

Does anyone know what that magic X hours / minutes is?

Note: I usually get up every 25 minutes to just swing my arms and walk around for half a minute.