My ex's family ran several chinese restaurants... I've also done chinese cooking, etc. MSG is from starch, sugar beets, sugar cane, or molasses. It is best to ask chinese restaurants to not use it when ordering a dish if you have a known allergy. Some products do contain MSG others don't only way to know is to read the bottles. I think oyster sauce does contain it but some soys don't.(there is light soy, dark soy, and mushroom soy).

_{/me goes and checks the labels in the fridge as I happen to have all 3 types for cooking...}

Out of the ones in my fridge: 1 light soy contained 1% MSG and another perservative(it was a japanese light soy that I use for sushi). 1 light soy had no perservatives. The dary soy and mushroom soy also contained no perservatives. Also checked my teryaki marinade and it had 1% of a diffrent perservative but not MSG. Tho my soys aren't low sodium you can get low sodium soy sauce and probably low sodium soys with no MSG. While I don't have any on hand I think oyster sauce however commonly has MSG.

Here are two msg websies... one pro one con:

The Discovery of Umami - MSG Info

National Organization Mobilized to Stop Glutamate