Examples of potentially novel proteins are venison (deer) and kangaroo meat. When you talk with your vet, tell them the protein source in each food you have fed your cat.
[header] How to put your cat on a limited ingredient diet [title] Talk with your vet. [step] A limited ingredient diet has ingredients to which your cat is not allergic. For cats, this diet typically contains a novel protein, which is a protein your cat has not eaten before.