The only food that CJ is able to eat is Science Diet D/D Green Pea and Duck. Every single other food did not agree with his precious little sensitive tummy, and even this food doesn't agree with him sometimes. Science Diet also has Z/D which is supposedly good for cats with allergies - did nothing for CJ, but I know it has worked for many other cats. Both of these you can get through a vet only.....or maybe online(?). They will be more expensive than the Purina One.