Maybe the fiber produces butyrate which is healthy for the gut lining???

Low carb ketogenic diet produces betahydroxybutyrate which is healthy for both the gut lining as well as the heart and brain.

Maybe the body has compensations to allow for different diets. To make use of inputs that may be less than ideal???

I am not saying there is only one way to do things. There are probably multiple ways to skin a cat. Some ways may be more appropriate for some people than others. Each of us should pick the best for ourselves.