That's exactly the hell… they aren't sure.. so actually I have to say that after the Purdue study years ago, nearly all my Rottie, chow, Dane and other breeder friends got rid of elevated bowls as NO evidence they helped at all and some they might.
The RAW diet website says to not feed a combination of raw and kibble as the kibble takes so much longer to digest and is likely to cause stomach upset.
They do and it's silliness. Not one single shred of research, not one, backs it. Pseudoscience bothers me, especially pseudoscience made up to get you to feel bad about not doing things they way they want you to. Especially ALSO when that nonsense causes people to not TRY raw because they cannot do it all the time and are told it is bad. I fed both most the time for 15 yrs, as do most of my friends. I wish I had the time and money to have done nothing else back then. I cannot do raw now as I have one dog with autoimmune issues and another who, no matter the meat source, every time I try she gets diarrhea. Sigh. So I feed the $60 per 25 pound best dry I can, with lots of home cooked meat, salmon ears and US source/made chicken treats. But I believe in raw in any situation where you can.