Claims suggest that soluble and insoluble fiber is beneficial for the gut. If one has to supplement fiber, either one, to their diet, something is awry. 
Poop potions, imo, is an industry all on its own. They are capitalizing on, uh, the hardships a lot experience due to the SAD. 
I’d venture to say that a carnivore diet that’s consumed with a lot of the animal fat doesn’t cause problems. 
If one is consuming milk and cheese only, then yes… let’s talk fiber 😂