Doesn't acid dissolve the food, whether fruit or meat? I think we need acid in the stomach to achieve this goal. I agree that meat will produce more acid to break it down, and that isn't good, but acid, I believe, must be present in the stomach for proper digestion. Animals even have stomach acid and they are on a natural diet. Large cats, lions and tigers, for instance, have stomach acid that is 15 times stronger than ours to break down the red meat they consume.
Granted the SAD makes our bodies work harder, but acid seems very logical to have in our stomaches.