On degradation of the nutritional value, it all comes down to the same process by which we get the caloric value out of the flour, oxidation. Flour has several orders of magnitude more surface area by weight than wheat berries do, so oxygen has more access to do it's work. Storage with low oxygen permeability (mylar, steel, etc), low light (which affects surface temp, every 10*C temp rise doubles chemical reaction rates), low oxygen presence (O2 absorbers, vac sealing), and low temp (again, chemical reaction rate) will preserve the nutritional value longer.
/EDIT: Forgot moisture- water is H2O, and the O (oxygen) can break off to do it's oxidation gig. Water is just oxidized hydrogen. Worse yet, breaking down starch (C6H10O5)n gives you, basically, CO2 and H2O.
FWIW, this works for pretty much storage of *everything*. You wanna store things forever, put 'em in a electromagnetic free, absolute zero vacuum* with no tidal (gravity change) effect.
/Of course, then you have sublimation... Can't win 'em all.