Over the years, I have used a variety of prescription foods....Hill's, Purina and Royal Canin and they have always worked for whatever condition a pup had. The only time they did not was IF there were two different conditions. I can assure you that there is nothing unhealthy about those foods....quite the contrary. They save lives!!! In those cases where there were various medical issues and no RX food to cover them all, I consulted with veterinary nutritionists and home cooked for them.
I am going to copy/paste my response in your other thread:
I would suggest a consult with a vet nutritionist. He should not feel hungry all of the time! You might want to consider home cooking. I have done that with pups who have multiple issues that it is hard to find an RX food for. I have a pup with lymphangectasia who needed a low fat diet...she loves her home cooked diet and never is hungry. It ended up being more food than she had ever eaten and she maintains her weight on it. She is a happy girl and has done well now for two years on this diet. It was formulated by Dr. Catherine Lenox, a vet nutritionist in Houston. (you could do a tele consult with her)
Dr. Rebecca Remillard, a vet nutritionist, has a website PetDiets -
www.petdiets.com that has a lot of information. You could also do a consult with her for a home cooked diet.