My hair Medium/fine hair responds well to protein the right amount.
While trying to figure out what was the right amount for me...I over did it with the protein. My hair felt like straw....dried out straw. What wave I had was all but gone.
I recovered by laying off the protein for a while and using lots of moisturizing products.... DT, leave ins etc. My hair does look fine now. But I limit my PT treatments to 2x's/month.
You may need more or less. If you do go overboard with the protein, your hair can recover.