@izakb I have always fed grain inclusive, even though I got my first dog as an adult in the peak of the grain free thing, simply because that dog does better on grain inclusive foods which have more fiber. My spouse has fed raw, which I have always vetoed for sanitary reasons — it's terrible for passing Salmonella to humans — and their dog at the time did fine on it. I have known dogs to do very well on a wide range of diets, and I have known unfortunate dogs who did not seem to be able to digest much of anything. A good breeder should select against those latter dogs as much as possible.
The problem with grain free diets is probably indirectly a function of cost. Kibble manufacturers are trying to make kibble as cheaply as possible so they can price their product lower or their profit higher. In a grain inclusive kibble, a large volume of the diet is made up by comparatively cheaper grain products. In grain free diets, manufacturers need something to replace that enormously cheap (relative to meat and fat) component with. It should be a binder and help hold the kibble together. It should have a particular ratio of protein to carbohydrates.
While there are grain free kibbles that are ostensibly 100% meat (they're great for training treats), these are about as spendy as feeding raw... because you're actually feeding that much meat. In order to compete with grain based kibbles, manufacturers had to replace that grain with something inexpensive to take up the space. Potato and sweet potato were early favorites, but they were too obviously swapping one starch for another. Pulses, now—lentils, chickpeas, peameal—are TECHNICALLY not grains and therefore are grain free. And they're cheap, almost as cheap as grain! This quickly became a dominant formula for grain free chow. Even better: pulses are higher protein than meat, so you could provide a higher ratio of pulse to meat and still remain within the AAFCO guidelines.
... And then came that cardiomyopathy study a few years back. 2018, was it? I felt real smug over that when the data came out (although it wasn't why I was feeding grain inclusive). It quickly emerged that the problem was specific to kibbles that used pulses as fillers and particularly protein bases.
Essentially, it's probably a good idea not to feed your dog huge quantities of peas and lentils and beans, but other than that... If they do well on a commercial diet, go nuts. Adding food isn't a problem unless they get fat. If you make a diet you are going to have to put in a lot of work and effort to pull it off.
Fortunately for our wallets, there's no reason to believe that dogs, or for that matter humans, should be eating that much meat. In fact, we have strong evidence of selection to tolerate and even rely on grains in the early evolutionary history of dogs.
Anywayine, mine came eating Nutro. I switched to Purina Pro Plan because I've had consistently very good results with it and it's not manufactured by Diamond and doesn't get recalled much. Quality control! But I don't see anything wrong with feeding Nutro. I wouldn't feed small quantities of diatomaceous earth, either—I use dewormer—but I'm not going to tell anyone who does choose to do that to stoppit.
