General rule of thumb: Any diet that does not promote bowel motility, will usually inhibit it.
In around March last year, I went on a largely Ketogenic diet. The diet is low carbohydrate, high fat, high protein. It wasn’t long before I started doing some impressively firm poos. I’ve relaxed that diet a little, and my poos have become a little softer.
Lots of cheese and refined carbs (pasta, rice, white bread). Also take Loperamide to clog yourself even more. Let the log sit and “bake” for a few days in your colon. You will get delicious rotten smelling farts, that satisying full feeling, and a big fat solid log at the end.