This is my humble opinion... two things present in all Kibble (except for one that I know of) are far more detrimental to our dogs' health then we think... Ingested daily, these are viewed as toxic and life shortening.
1) Flavour Enhancers = chemicals, not naturally digested by the body but they make the food desirable. Think Chicken McNuggets and children.
2) Preservatives = how do you think a bag of food can last up to a year (even after it's opened)... these chemicals slow down the digestion process and as a result, don't get truly eliminated from the dog during digestion.
This morning an 11 year old shih tzu came in... his skin is slightly better than it was this summer. He was flakey,itchy and unpleasantly smelling... and all this was a big concern for his mom. So she had a long chat with her vet and he highly recommended 'medical' from Royal Canin (another popular kibble recommended by vets).

Food is Medicine
Carna4 Ingredients: Fresh Chicken, Chicken Liver, Eggs, Organic sprouted seeds, sprouted barley seed, wild salmon, whole peas, sweet potatoes, amaranth, ground whole brown rice, organic sprouted lentils, potato starch, organic sprouted flaxseed, whoe apples, sea salt, kep, rosemary, parsely.
I did a quick lookup to see the make up of the ingredients and discovered.. shockingly... this food is loaded with low quality ingredients... aka, it's probably highly profitable.
Food is not Medicine: Royal Canin Skin Care - Ingredients listed in order of quantity:
Brewers rice, chicken meal, corn, brown rice, chicken fat, natural flavors, wheat gluten, dried beet pulp, rice hulls, brewers dried yeast, dried egg product, fish oil, calcium carbonate, potassium chloride, vegetable oil, sodium silico aluminate, L-tyrosine, fructooligosaccharides, salt, sodium tripolyphosphate, L-lysine, choline chloride, taurine, glucosamine hydrochloride, vitamins [DL-alpha tocopherol acetate (source of vitamin E), L-ascorbyl-2-polyphosphate (source of vitamin C), biotin, D-calcium pantothenate, vitamin A acetate, niacin supplement, pyridoxine hydrochloride (vitamin B6), thiamine mononitrate (vitamin B1), riboflavin supplement (vitamin B2), folic acid, vitamin B12 supplement, vitamin D3 supplement], green tea extract, trace minerals (zinc oxide, zinc proteinate, ferrous sulfate, manganese proteinate, copper sulfate, copper proteinate, manganous oxide, calcium iodate, sodium selenite), chondroitin sulfate, rosemary extract, preserved with natural mixed tocopherols and citric acid -
See more at: http://www.royalcanin.ca/index.php/Veterinary-Products/Canine-Nutrition/Veterinary-Care-Nutrition/Dental-Dry#sthash.2s5JGbW0.dpuf