Tricky doctors advice.
He's maybe trying to see if the fibre helps your diverticulitis. I don't know.
That's the trouble with changing many or several things at once. I am not sure what I'd do if in your situation. Maybe the fibre and Metamucil would be enough to settle your problems down altogether without going gluten free?
It's like one or the other to me but I really think you should call the Doctor or ask the nurse at the office? Your Doctor has perhaps never gone gluten free so doesn't realize what's involved.
Maybe he thinks doing all 3 will settle you down faster and that's the primary goal I suppose.
When my daughter started going gluten free we were astounded at all the products that contain gluten. I threw out so much even in the bathroom products. It was very difficult at first. She started suspecting gluten sensitivity when she kept breaking out in a rash around her mouth and chin. She also had tummy troubles. Then when she stopped eating gluten products that all cleared up... plus she is particular with the bathroom products. She cheats a little from time to time but always breaks out in the same rash the next day.
Have you read The Gluten File, jewels?
It's in the Sticky threads at the top of the forum.
btw I think Metamucil powder is gluten free but there are Metamucil wafers that contain gluten.