My Lady doesn't have a shunt, but she's been on seizure medication for nine years and it's damaged her liver. She became a very picky eater until I changed her diet. Liver compromised dogs still need protein as too little can actually damage their liver. They just need high quality protein preferably from dairy products like eggs, cottage cheese and tofu.
This is a great resource for liver friendly foods and sample recipes.
Liver | B-Naturals.Com Newsletter
This is Dr. Center's Tofu and Rice diet:
1 lb tofu, 2 lbs cottage cheese, 4 cups cooked rice, 6 T safflower oil, 1 tsp salt substitute, 6 tsp dicalcium phosphate, 1-1 tsp pectin. Can use a strong low salt cheese to flavor. (Center S. A., Reynolds, A., College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853).
Vegetarian kibble is also good. Petsmart carries both Avoderm and Natures Recipe vegetarian varieties.