After doing a bit of research after a thread started regarding diarrhea I figured out all the foods that caused looser stool or diarrhea in my cats had egg product. Just thought I'd throw that out there.
Eggs contain lecithin, an emulsifier, which helps fat become liquid and fluid. This speeds up transit time resulting in loose stools or diarrhea.
The devil is in the dose. You can use a very small amount of egg yolk to manage hairballs since it's fat that binds hair into an impassable ball. When that fatty hair clump is too big to pass out of the stomach, the cat will eventually have to bring it up. Depending on the cat, this dose can be as small as 1/8 tsp to break up the fat that's binding the hair. More than that will give my Krista loose stools.
Out of curiousity I went through a lot of the diarrhea threads to find out what was being fed and I found a vast amount were being fed foods with egg, egg product, or egg whites. BTW, I wish people would list what their cats were eating on there first post. I'm sure a lot of diarrhea was caused by parasites or other issues, but maybe a simple ingredient was the cause.
I just started feeding foods with egg to my senior cat who has issues with constipation, hopefully this will help so I don't have to continue adding fiber and probiotics to his diet