The grains and products used in Dog Foods is more pure, more sterile, etc. than human grade grades/foods.
Human grade foods will starve an animal, they are the most mineral deficient grade and usually the most mouldy, etc. ANIMALS would loose their hair, have cancers, kidney problems and gain allot of weight on human grade foods and the farmers andanimal lovers would stop buying such poor foods. So the dog food companies have strict guide lines for buying food for their products, while all the trash left over goes into human foods.
I don't suggest people eat dog foods, but I have known some that have. If you go to your local farm store you might find doggy biscuts that can correct an old arthritic dog that is dragging its legs behind it, go into your local drug store and ask them if any such product exist on this planet nd they will advise you to your local MD and we all know their path.
Those reading what I call BOOK III learn maybe too much about animal grade medicines.