Honestly, and this is the truth, a cat's digestive system is meant to handle meat almost exclusively. Sure they do nibble on grass occasionally, but that is a mechanism they have to combat digestive upset. Its like a human taking Pepto Bismal.
Nowhere is there a means to handle grains. Grains only cause allergies, digestive problems and urinary tract problems. Only buy a cat food that has quality meat as their first ingredient. No bi-products, no meal, just simple and plain beef, chicken, or fish pieces included.
Be aware that anything sold in a grocery store is usually low quality and has corn listed as one of the first ingredients, if not the first. Corn is primary used as a filler, so the food is less expensive to make. Also be aware that corn is also the cause of a lot of health issues in animals. Its high in sugar and low in nutrients. Its a grain, plain and simple and a low quality grain at that. Also be aware that the corn put into a cat or dog food is not processed and therefore has a high probability to contain chemicals and such (as was the source of the huge pet food recall of some odd years back, they, meaning China, had used unprocessed filler ie. corn and such, which contained a chemical that, when ingested, caused severe illness, sezuires, and even death in dogs and cats).
The best diet for a cat is one that is high in animal protein, or meat. A cat NEEDS animal protein to function properly. No ifs ands or buts about it. Its how the evolved, its how they are. Don't go trying to change that.
I recommend Blue Wilderness, or anything with the Blue label. Also, Wellness, or any high quality holistic food is a good brand. Just make sure there is no corn or grains in the food. No canine or feline diet with grain is very nutritious.
“The day the power of love overrules the love of power, the world will know peace.”
― Mahatma Gandhi