They had a narrower grouping of bacteria as plaque on their teeth. And obviously that bacteria was less harmful to their teeth. So I'd guess that eating a narrower group of foods, without grains, is good for teeth health, and the body's. Are they going to try to determine what that bacteria was, and from where it came.
I have the sense, though, that we acquire a lot of bacteria just from the air and soil around us. To be as pure as they were, we'd have to move into a virgin forest or field.