How is King Arthur bread flour made?
They make whole wheat flour, but their bread flour is definitely refined; it does not contain bran or germ. Their bread flour is milled from a specific hard red spring wheat from North and South Dakota. That particular wheat is higher in protein than the wheat and wheat blends of other brands of bread flour.

KA's whole wheat flour (not the white whole wheat) is also milled from hard red wheat, but it's unclear if it's the same "hard red spring wheat" as in the bread flour. The protein level is higher in the whole wheat flour than in the bread flour.

 

Notice that the bread flour is enriched (see the ingredients), as is required by US law for refined flours. The whole wheat flour is not enriched.




You might find this information regarding whole grains helpful: What is the meaning of the term whole grain? Notice from the graphic that there is not a lot of protein in the bran and germ.