What food should I switch my cat too?

She is currently on Authority Indoor cat food from Pet Smart, but she is shedding all of the time, and always has almost 24/7 365. So my vet said this is not normal even for long haired cats and that she is missing fatty acids, or amino acids something like that. He said we should switch her food, and I know I need to do it slowly over time, but i'm not certain what the best food for her would be. She has been on authority since we adopted her 3yrs ago as a kitten, she went from kitten authority to adult. She has always been very healthy, even with the shedding she very rarely gets hairballs, and doesn't have any bald spots, it is more like spring shedding just all year round. Any help would be greatly appreciated.