What is a healthy low fat name brand of cat food for an adult cat?

I was shopping for cat food and and I was told eukkanuba is a good brand, but noticed 21 % fat content. I noticed the previous brand I was using, Whiskas, had less than15%. Is buying pet food from the pet store causing more harm than good for my cat..Anyone else counting calories for their indoor cat. I would like to know what the better diet would be. She is not overweight.