You never know when you might develop an allergic reaction to something and the same goes for cats.  If your cat starts to groom and scratch a lot, she may have developed a feline food allergy. In pets, food allergies often manifest themselves in the skin. They can also cause vomiting and diarrhea.  If your cat displays these symptoms, take her to the veterinarian.  If your vet confirms that it is a food allergy, not an allergy that is inhaled, he or she may suggest that you change your cat’s diet.  The culprit is usually protein. Feeding a new source of protein usually alleviates the problem.  If not, pet medication may be needed.