The bending moment is produced by the lift generated by the wings and the weight of the fuselage in the middle, or on the ground the weight of the wings and the support (gear) mounted on the fuselage or fairly close to it. So it is always there.
The only choice you have is how to build the structure to carry that load. You can:
- Have a central spar, a solid beam that carries the load, and unstressed or lightly stressed skin. That's how all the early planes with fabric-covered wings and fuselage were built.
- Have a hollow wing with stressed skin supported by mesh of ribs and longerons. That's how most aircraft are made today. You have tension load on the bottom and compression load on the top and the centre is not doing much, so not having it there makes a lighter structure.
- Anything in between, with solid spar, but some load carried by the skin.
Independently of that, you can
- Build the structure in one piece and and attach the fuselage to it (from above, below or build it around).
- Build the structure in several pieces and join them with rivets, bolts or glue.
In either case the structure is continuous through the fuselage. The fuselage walls would have no chance of handling the load if you didn't have any connecting structure inside and would bend easily. The only difference is whether it is joined from multiple pieces or not.