Originally posted by Akateros
Both whole wheat flour and stone-ground ww flour are made from "the whole grain, and nothing but the whole grain" as it used to say, and maybe still does, on the Shredded Wheat box. In theory, the stone-ground flour (if really
stone-ground the old-fashioned way) would not have reached as high a temperature as flour milled by more modern methods, which preserves more of the fatty nutrients, particularly in the germ.
(All whole-grain flours, whatever whole grain they are, incidentally, should be stored cool, even in the fridge or freezer if possible, and bought in small amounts and not kept lingering about too long, to prevent rancidity.)
Buckwheat is nothing to do with wheat at all. In fact, it isn't even really a grain. It is the seed of a plant related to rhubarb. It does have a strong flavour, and also lacks gluten.
Oats, or oat flour, can be substituted for wheat flour in certain circumstances, but use discretion. For one, they lack a certain structural integrity (again, the gluten content) and for two, the texture's different.