The Load Factor is defined as the proportion between Lift and Weight, where the Lift is that part of the force exerted by the wings perpendicular to the flight path.
The load factor in straight and level flight is equal to one, as the Lift must oppose the Weight. Any aircraft in a steady climb or decent required less lift than the straight and level case. (Sounds strange, I know.)
Consider this: as you sit in your chair at your computer, you are experiencing "1 g", all of which is through your seat on the chair. If you now tilt your chair back onto its rear legs, then you are still experiencing "1 g", however, the force is now shared by the seat of the chair, and the back.
It's the same with aircraft, tilt the aircraft back (in a steady climb) and the force is now shared between the thrust and the Lift. Tilt it forward (in a steady descent) and the force is shared by the Lift and the Drag. In either of these cases as the Load Factor only considers the Lift then the Load Factor is reduced.
Same applies in a descending turn or climb.
As an aside, your stall speed is reduced in a climb or descent for the same reason. The stall speed in a verticle climb (no lift required) is zero - something all aerobatic pilots (performing "Stall Turns" or "Hammerheads") know.