From everything we know about hair science, protein in and of itself cannot straighten hair. Only breaking disulfide bonds will do that and protein alone doesn't have the capability.
The treatments I checked out had a little "secret" ingredient in them...akin to formaldehyde. Surprise, surprise. And when I asked the keratin vendors at Premiere Orlando some very pointed questions on how the process works, I got a lot of hedging and deflecting.
Of course, I'm probably still pissed because one of the keratin salesmen looked at me and enthused, "You'd be a perfect candidate for this!" And I pointed to my head of non-frizzy, shiny, virtually perfectly-formed spirals and said, "Are you telling me you think I look like I need a straightening treatment?" The frantic backpedaling that ensued would have been comical if I wasn't so insulted, lol.
Without exception, every single person with coarse hair I talked to who had this done said their hair was an unmitigated disaster afterward...just like broom straw. No surprise there, either.
~ aka 'StruttsWife' on naturallycurly.com