Seems unlikely that dog food is the issue, else they would have caught it by now. Dogs don't take well to quick changes in their diet either (they'd start showing some of the symptoms described), and the list of foods they shouldn't ingest is long. Recommending that people start feeding their pets human food would probably just make the whole situation a lot worse.
If it were from contaminated food you would expect it to happen more abruptly, then taper out. No common food link has been found either.
Could it be food allergy?
If they come across enough food, they will eat until they puke, sleep for an hour, then eat their own vomit.
It's no controversial statement that dogs and humans have different preferences in food.
Cats are carnivores. Dogs are opportunistic carnivores. They prefer meat, but can survive on plant material.
> Well, dogs are proper carnivores who can eat raw meat or fish stored at room temperature for days, without any problems.
Yes, but only because they don't know better. Our digestive systems are better than dogs, although dogs are efficient at killing some pathogens(stomach PH is way lower). So they may fare better on not getting infected by stale food, but their systems will still have more problems trying to digest food full of toxins.
There is an enormous list of things that dogs cannot process (or are toxic), but we can. A lot of it is due to our liver. Dog's livers are... dog shit.