Fuel cell system and method for operating a fuel cell system

Upstream from a fuel cell unit (2) there are devices for adjusting pressure in a gas generation system (5) and/or a mass flow rate through the fuel cell unit, so that pressure can be reduced at least short term during change-over from a partial load area to a full load area and so that pressure can be increased at least short term during change-over from a full load area to a partial load area.