I don't think the research shows that at all. Not sure where you are getting that from. The good gut bacteria love fiber. Meat = ZERO fiber. Fiber also gives poop its firmness. Non contaminated, non farm raised fish with lots of vegetables would be pretty good for you and your poop.  All fish, with zero fiber, what is there to "bulk" up your poop? Of course it is going to be a runny mess.  A fatty would just want to take a pill to fix that instead of changing their diet. Whereas a reasonable person would understand his diet is causing a problem.