Hi, I've been concerned about this and have been doing a lot of reading, from which it seems conclusive (to me, at least) that this blanket 'grain-free' fad can be dangerous to dogs' health. Not all dogs, of course. Particulary those who are closest related to the wild, grain free seems the best advice. But for those dogs who are dogs, i.e. who were domesticated tens of thousands of years ago, it can be a totally different matter - depending on the breed. There is a lot of reading and information out there, and it will take you on to a very interesting path of discovery. The long and the short of it is that dogs, like people, ate whatever was available in the region where they lived in with their human companions. So if they lived near the sea, seafood will have featured on the menu. If they lived in the forest, rabbit, fowl, venison.... Etc. In any case, over all those millennia their systems will have got at least used to whatever the available food was. I'm not a scientist, but it seems reasonable to assume that in some aspects their systems will have even started to require some of these foods to remain healthy.
I will only cite you the example of my Dobermann Meg. No one quite knows which breeds Mr Karl Dobermann used to create this beautiful, intelligent, kind dog, and how high the percentage is that each of these are present in them today, but there are a few likelies. The German Shepherd is one, Rottweiler another, and there are few others. When you look up these breeds on the scales that show how well or badly they can digest grains, they score very highly. In short, these are breeds who at the very least have no trouble digesting grains. And if you then read the FDA study regarding the effect grain-free diets may have on DCM....
But the same argument goes for a diet that is entirely based on raw food. That seems just another fad. Dogs are not all wolves. It's nonsense. Apart from those breeds that are still close to the wild, dogs are dogs. Depending on the breed they'll have been eating a mix of cooked and raw for many millennia.
But I urge you not to take my word for it, and to do your own reading. Good luck!