Dark soy sauce is full of msg. Is there another substitute that is healthy ?

Well, first of all...MSG isn't any more unhealthy than regular sodium. MSG metabolizes into its components in the body: sodium and glutamate (which is a natural amino acid that the body requires). Now, if you're trying to live a lower-sodium life (which is a good idea for most people), there is low sodium soy sauce out there. Dark soy sauce is usually more for color than anything else. It has a distinct flavor, but its not necessary to the success of a dish. I would either replace it with low sodium soy sauce or just leave it out.