There are a lot of quality holistic foods with no added preservatives, grains, or fillers to choose from. Added grains (rice and oatmeal are acceptable, though not as good & easy to digest as potato) & fillers are pretty much indigestible, hence there is little nutrition absorbed and added bulk in the waste. Added preservatives and sugar based ingredients could cause cancer or other issues.
Just please stay away from:
Corn, Corn meal, Corn Glutton
Wheat, Wheat GluttoWheat, Wheat Glutton
Rice Glutton, Brewers Rice, (white rice is acceptable though not great)
By Product, Most Meals (cii-theme-font: minor-latin; mso-fareast-font-family: Calibri; mso-fareast-theme-font: minor-latin; mso-hansi-theme-font: minor-latin; mso-bidi-font-family: "Times New Roman"; mso-bidi-theme-font: minor-bidi; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">if they are the main source of protein, as they have high gas they have high ground bone/beak content – though fish meal is ok)
Propionic Acid (a preservative)
Here are some known good brands (in no particular order):
Flint River Ranch
Blue Buffalo (Wilderness is best) - just found out caramel is in their life source bits - if your dog has cancer do not feed them this food as sugar can cause cancer to multiply - they were not willing to remove it.
Taste of the wild