For my dedicated poop eater, it was definitely diet, not amount of food. He stopped completely when I switched to better foods and hasn’t gone back since. For him, I think it was either the whatever digest that they spray on the kibble for flavoring or too many carbs. Some ingredients are nothing but a way to hide MSG in the food and I read that some believe that this “flavor enhancer” enhances poop too. I switched to higher protein at the same time and that would affect the “flavor” too, so I can’t really say which did the trick.
