[BeckyBeagal]

Dogs are carnivores
All scientific evidence points towards the fact that dogs, while not true carnivores, are opportunistic, carnivorous scavengers. Cats on the other hand are true, obligate carnivores, requiring animal protein to survive. There is a difference between a carnivorous scavenger and an omnivore though - dogs lack the dental characteristics, longer digestive tract and specific enzymes of true omnivores like humans. That is the reason why they can not digest grains and vegetables unless they are "predigested" by processing, mincing/grinding, or fermentation through enzymes or bacteria. Once converted, they are fully available to the dog.

This does, however, not mean that your dog will thrive on a diet mainly made up of poor quality grains or grain fragments, which is what most cheap foods are. Whole grains, including their entire complement of nutrients are much more valuable - and this does not only apply for a dog's diet, but for humans as well!

Cooked/processed protein is unusable for dogs
Common sense dictates that if this were the case, any dog fed either a commercial food product or a home cooked diet would die from malnutrition within a few weeks. Protein is the second most important substance the body is made up of, right next to water - accounting for about 50% of the dry body mass. Dietary protein contains the 10 essential amino acids required for building and maintaining muscle, hair, bone and organs and supporting other vital functions. Essential means that these substances must be supplied in the diet and can not be synthesized by the body.

The blend of protein sources is very important. Different ingredients contain different amounts of amino acids, both essential and non-essential. A product that relies on only a single source of meat (for example strictly lamb based diets) must be balanced by supplying other sources of protein, like whey, alfalfa, potatoes, or grains. The grain ingredients should not be the main protein source though, but only balance the profile of amino acids.

I've always fed __ food to my dog and he did just fine
While there is nothing wrong with feeding a particular food if your dog does well on it and you feel comfortable feeding it, the question is whether you have a basis of comparison and whether the formulation of the food has changed over time. I have seen the effect a better food can have on my own dog. When I adopted him from the shelter, he was a thin little puppy with a brittle coat and a rather strong "doggie odor". I didn't know better yet, fed an average quality food and thought the change in his appearance was stunning, except for the severe reactions he still showed whenever he picked up the occasional flea and got bitten before it died. He had gained weight, the odor improved and his coat was softer and shinier. I was happy and didn't think that any further improvement was possible - until he had been eating a really high quality food for about a month. His allergy to flea bites disappeared entirely, the muscle tone became much more defined, his coat even glossier, softer and most important, much, much denser. The doggie odor vanished.

If I hadn't at least given the better food a try, feeding it long enough to see results (depending on the individual dog this takes about 4-8 weeks), I would still have been convinced that my dog "did just fine" on the lesser quality food. Now I clearly see the difference between "doing just fine" and truly thriving. Every step up the "quality ladder" will bring improvements, the stray dog who used to survive mostly on garbage will do better once he gets a daily ration of even a relatively cheap food because it supplies more essential nutrients; and a dog who was fed a grocery store brand is guaranteed to improve on a better quality product as well.

Fat supplies only empty calories
Far from the truth. Fats are highly digestible, very palatable, and are an energy dense nutritional ingredient which is essential for healthy coat and skin, reproductive efficiency, kidney function and the absorption of the fat soluble vitamins, A, D, E, and K. It is the main source of energy - one gram of fat supplies 2.4 times the energy of one gram of protein or carbohydrates. As a less well known fact, fat also serves as a metabolic source of water, so a hard working dog is less likely to get dehydrated when fed a diet higher in fat. Fat metabolism produces 107g of water for every 100 grams of fat. Protein produces 40g water/100g, and carbohydrates produce 55g water/100g. The fatty acid ratio is important for reducing the production of inflammatory mediators in the dog's skin, plasma, and neutrophils (a type of white blood cells). Omega-6 to omega-3 fatty acid ratios of 7:1 or lower are optimal.

Pork should not be fed because it causes pancreatitis in dogs
A statement I have encountered quite often recently, unlike any material that substantiates the claim. According to veterinary literature, the most common causes for pancreatitis are

a high fat, low protein diet
obesity
trauma (car accidents, falling)
other diseases (Cushing's syndrome, diabetes)
tumors
some drugs and toxins (e.g. antibiotics, insecticides)
genetic predisposition (hyperlipidemia, e.g. mini schnauzer, cocker spaniel)
As part of a well balanced diet, pork isn't any more dangerous than beef, lamb or chicken. The fat content is key, and many pets suffer from pancreatitis when fed excessively fatty, greasy table scraps - which are not part of a balanced diet. The most susceptible animals are those who don't eat anything but kibble all year and suddenly get an overload of "goodies" on thanksgiving or other holidays.

One other thing that doesn't quite fit the bill is the fact that there is a good number of premium quality dog foods that use pork meal as a protein source. I very much doubt that a single manufacturer out there would risk their excellent reputation by purposefully including an ingredient in their food that is a proven cause of pancreatitis.