Neutralization

As we all know, digestion begins from the mouth, and saliva is alkaline. There are acids in the stomach. We must not eat anything acidic/sour along with our meals. The saliva neutralizes it and hence, this leaves less saliva for "the actual food". You might have noticed that saliva gets thick at the back of your tongue once you have drunk nimbupaani :) :|

The reason behind the papads

What we are meant to digest, we digest easily. And a simple test of checking that: soak the thing in water. If it disintegrates and dissolves, it is digestible. Papad, even if you soak for 20 days does not disintegrate. Implies papad is baad for health