Protein degenerates with heat...but....heck, if the degeneration with heat is bad for us, we'd have to eat all our protein foods raw

So, yes, it does *degenerate* but don't worry about the nutritious value. The label warnings are more because the change in texture will be yucky for most of you. If the protein powders lump up and hardens (which it will with heat unless you mix it quickly and well with hot water, or mix it into cold water, dissolve, and stir while heating) it can get hard to tolerate.