Actually, I heard it was the other way around - high protein causing kidney problems. It was a big argument against raw feeding way back when.

Flaxseedoil1000, you raise a valid point and while GOOD by-products are certainly benefitial and essential in a dog's diet, an ingredient's list does not do a food justice, or lack thereof. You don't know whether by-product means livers and hearts or beaks and feet (btw, I know poultry feet are a popular raw food item). You don't know the quality. You also don't know the AMOUNT of a said ingredient in kibble. You get a general idea of which ingredient dominates the kibble, but you don't know exactly how much of said ingredient is in it. An ingredients list is so vague and generalized, it is difficult to judge a kibble based simply on the ingredients list so much of this is up for debate.

However, as a general rule, dogs are carnivores. Therefore, it is unnecessary to include carbohydrates into a dog's diet (both simple and complex), i.e. corn. As well, while carbohydrates are a worthy source of quick and efficient energy, lipids and proteins would do a carnivorous dog much better.

You also mentioned that plant based proteins are troublesome and do not provide a viable source of protein. Therefore, the rest is thrown out as waste. Does that not sound like filler to you? While a certain amount of carbohydrates may be acceptable and even beneficial to a dog's diet, they should NOT make up the bulk of the diet. This is why I must agree with MyPeanuts. Corn as the number 1 ingredient is something to avoid and I do believe it is considered a filler when it is used so blatantly to fill up space.

There are many variables that may affect the quality such as the cooking temperatures/times, quality of ingredients, etc. However, I truly believe that corn (and all parts of corn) and byproducts as the first ingredients is a signal that the company is trying to fill the kibble up with cheap ingredients. This is just my opinion. The Food Debate was named so for good reason