And there are few things that people are more dogmatic about than what they think is best for their pets.
Most of the advertising, discussion/promotion of ingredients, promotion of benefits of certain benefits, etc. is aimed at marketing to people. Obviously, dogs do not make decisions on what type of food is purchased for them. Because of this, many trends in pet food and ingredients are based on popular assumptions and not on science. For example: 40 years ago, the main protein source in dog foods was either chicken or beef. When veterinary dermatologists were suspicious of a food allergy or intolerance, they would suggest feeding a protein and carbohydrate source that the dog had not been exposed to previously. Lamb and rice was the usual recommendation, because none of the commercial dog foods had lamb or rice as an ingredient. Then, some dumb-ass decided that they would formulate a commercial pet food with lamb and rice and use the tag line that veterinary dermatologists recommend lamb and rice more than any other ingredients - so it must be better for your dog, right? Gradually, we could no longer use lamb and rice as a hypo-allergenic diet. We had to find other protein sources, and as quickly as we did the commercial pet food companies responded with their own. And the deep, dark secret is that the limited ingredient pet food that you buy in the store that advertises "no chicken (or whatever) used as an ingredient" has enough parts per million of chicken (or whatever) in it to elicit an allergic reaction. So now, we are forced to use very expensive hydrolyzed protein prescription diets to effectively rule out food allergies. (And, by the way, a food allergy trial can take 12 weeks of eating nothing but the prescribed hypoallergenic food - a single bite of something different will invalidate the entire food trial).
So it goes with many ingredients. By-products get a bad rap. Byproducts includes organ meat and all the other things other than muscle. As a whole, byproducts are more digestible and have more nutrition than muscle alone. Grain is not a problem for the average dog to eat. In fact, 10,000 years ago dogs evolved to digest grain better than their wild counterparts. I think that the current trend in grain free dog foods is aimed at the increasing numbers of people that are gluten intolerant (which I think is Monsanto's fault. But that is a whole 'nother can of worms).
There is no documented benefit to feeding a grain free diet to the average dog. Period. The current connection between grain free diets and dilated cardiomyopathy (DCM) is an accidental finding. Yes, the numbers of reported cases is small, and the causative factor is (as yet) unknown; but the fact remains that there has been a disturbing rise in the numbers of these cases over the past few years. This alone is enough to make me tell my clients not to feed grain free until this is sorted out.
SO what should you feed? And why? This is what I tell my clients: There is no one best dog food or way to make dog food. There is little to no regulation on the claims that a pet food manufacturer can make. "Organic" and "natural" are all but meaningless terms when seen on a dog food bag. A company that claims that they have no added "whatever' may be sourcing ingredients from places that add all kind of "whatever" before they ship. The only restriction is that an approval by AAFCO (the American Association of Feed Control Officers) cannot be put on a bag unless the company has gone through actual feeding trials and/or nutrient analysis. (we can get started on the validity of analysis for nutrients, but: 'nother can of worms...). So, there are many good pets foods on the market, few poor ones. I may love Brand A of food because of quality, reputation, etc., but your dog might not do as well on it as Brand B. This doesn't make Brand A "bad'. It means that there is an intangible difference in how your dog processes each food.
I personally like the premium brands because of consistency of ingredients. For example, Purina makes both Dog Chow and Pro Plan. The difference is more than just labeling. With Dog Chow, they use the commodity markets to buy the cheapest ingredients to make each batch of food (while maintaining equal nutritional quality); with Pro Plan, a more consistent recipe is used and is thus more expensive to make. As we seem to hear a lot these days, it is very simple.
Because of the long time in the marketplace, the commitment to nutrition research, and the willingness to own up to errors and make changes based on science, I tend to stick with the big names in the industry when making recommendations. This doesn't mean that I think that the smaller companies are inferior. With the huge numbers of brands on the market these days, there is no way that I can keep up with the relative nutritive quality of all of the foods. And I consider myself an expert compared to my clients. (Of course, many of my clients will disagree with this point, because they read something on the internet that counters my recommendation...)
My take home point is to look for the AAFCO label, and don't stress too much. And don't listen to anyone who says that "whatever" food is the best. It simply isn't true. There is nothing magical about Blue Buffalo, and Science Diet does not cause cancer. There may be some validity in changing brands periodically in order to average out any micro nutrients that may be in different foods (just don't try it with my dog - she will get diarrhea and poop all over your house). Home cooking a balanced recipe can work, but studies show that most people become lazy about preparation and ultimately feed an imbalanced diet (I had a patient that was fed on table scraps for years except had no thought to balanced nutrition. At age 12, the dog sneezed and bounced her jaw on the floor causing her mandible to shatter - the xrays showed that her bones were as thin as a piece of paper.)
Prescription diets are a subject unto themselves. There is a lot of documentation that prescription diets for a given condition can lengthen the life of a patient with that condition.
I guess that I didn't need the ibuprofen after all.