Some people, and perhaps many, have "sensitive" stomachs and need firstly foods with high fiber as in cereal grains such as wheat, oat, rice etc to buffer their gastric and intestinal digestive enzymes from accelerating the ER polymer break down thereby increasing rate of agonist release. Also depends on the ER Polymer physical properties that the Pharma is using for their opioid agonist.
High fibers are always recommended for opioid takers to prevent OIC as well as buffering.