Yeah kind of tricky,
Just a though - I also had/have parasites candida.....but could not tolerate many food cause of bacterial overgrowth SIBO and Protozoa. In which case several food actually made the situation worst . Maybe he could try the SIBO diet and see if any improvements.
Btw flaxseed also NOK for me. He should test and try...still no stool after 4 enemas hm...tricky