Searching for 'perfect' clean, nutritious, non-toxic foods for my babies has been a ongoing search of many, many, many years for me now.
Sometimes, it is not all that obvious what is 'wrong' with ingredients, either. I research each ingredient before buying the product. Corn, and other grains are not necessarily 'bad' even if they might be 'inappropriate' foods for the species...mine love to eat organic popcorn with me...but a few minutes researching what happened with "Starlight Corn" is quite enlightening.
Anything commonly GMO (corn, soy, safflower, canola, etc...and the list continues growing by leaps and bounds now) or anything 'questionable' or 'artificial' is to be avoided from my research...especially since there is no way to tell (although some mfgs do specify their product to be non-GMO) what's actually what as there is no requirement to share certain information with consumers. I stick as closely as possible to 'organic' ("clean"...natural...non-chemcial) ingredients, have even ordered special foods through health food stores when they were available years ago, and have spent many hundreds of thousands of hours researching this sort of thing...and searching for clean, species specific, pet foods for their health and my convenience.
I feel better, and they seem to, feeding mine from my own table the same as what we eat and supplementing with certain pet food items and only allow them a certain (tiny) amount of 'snack' and/or 'junk' foods...like you would do for any other child, if you're picky like me...if you know what I mean.