Hi My Husband Has Parkinsons Disease. WE Have Been On

Hi my husband has Parkinsons Disease. WE have been on the GAPS program fro about 6 months and have all benefited from it. He is having great difficulty with constipation. Even if he has fibre added like phsyllium husks (not sure how to spell that) it seems to get blocked in the large bowel. I am trying to get him to have a regular habit of taking something each day but dont want to upset his system. Do you have any idea?
Thankyou Caz :-)