I have just recently discovered that my hair is allergic to protein ;p had no idea, before, why certain products just destroyed my hair - but thanks to using Devacurl (protein rich) I finally figured it out.
My hair detests all proteins, especially wheat/soy/hops - these ingredients can result in a flash freeze of dried out, tangled, knotted hair within seconds of application...you asked how long it takes before you notice the protein destroying hair - I can go about 3 days using a protein shampoo or condish, or styling product, before my hair goes haywire - literally ;p first day of protein, hair loves it. Second day, have to rewash...no second day hair results. third day, hair goes limp; day 4, hair goes limp, gummy; day 5 - limp, gummy and greasy - day 6, instant hay, the moment I apply the product. Literally flash-dries my hair.
Coconut oil works very well as a deep condish, I melt a little organic coconut oil (about 3/4 of a cup) in a bowl over hot water, then apply to dry hair...cover with shower cap, blow dry shower cap for added heat penetration, then shampoo and condish as usual...results, awesome curl pattern that begins the moment I rinse out the last condish
I can literally see my hair doing a natural spiral and clump, and I only have 2 C hair at best!
My final conclusion is to avoid protein like the devil it is ;p and don't think just cause you may have fine hair, that you need it - I have super fine hair but lots of it, and my hair hates protein!