yes , the body maintains a small ph range , but it needs buffer alkaline minerals to do this
eating too many acid foods puts stress on these buffer minerals (eg magnesium)
And you can be too alkaline (alkalosis) and you can get too many alkaline minerals (milk-alkali syndrome).
you will find cancer thrives in an acid environment , look it up!
This is a complete myth. The cancer cells ferment leading to the production of acid. But the acidity has NOTHING to do with its ability to thrive. Unfortunately this myth, along with the cancer cannot survive in oxygen myth, keep getting repeated by sales sites.