A few of my cats have been sorted when they have had diarrhoea with Purina One which is dry, it was all our Timmy could have and he was fine on that, it has a high rice content I know some peeps would disagree about a mainly dry food diet but we were told to feed him that when we adopted him from the CP and sure enough most other things went through him. I know it won't work for all cats but I have heard of some other peeps whose cats have done well on that too when they have loose tums. eta: I should add that the cats I have now eat predominantly wet diet so I'm not suggesting a dry diet just that was what worked for Timmy.