As I rule I don't normally eat grains, cereal, bread and such ... I've been lax a bit now tho and probably until next year too! BUT overall, the less processing and refining the better because the nutrients are removed AND the starch will be so easily digested it could cause a glucose spike.
I think problems digesting whole grains is just that ... it takes more work to digest them than refined carbs. Of course, everyone is different and gender, age, health status, life experiences, cultural influences, etc., can all play a role in how we eat, digest, absorb and utilize our food and drink.