Or go to forums that are specific to your animals problem. In our case it was Epilepsy.
Our vet was who recommended Science Diet from puppyhood and then Phenobarb when the seizures started.
Thankfully, I found a few canine-epi forums (that happened to have enlightened vets on them) that recommended switching away from SD and go with better quality, non-corn-grain diets and higher quality proteins.
Within weeks, seizures dropped from 2-3 a week to 2-3 a month to 2-3 per year.
No Pheno. Found a new vet that agreed food is important.
We switched over said pups "healthy" mom too for convenience sakes. In a few months her eyes ran less, ears were much cleaner; less discharge, her coat was richer and she picked up energy.
Fromms.