The talk of glutamic acid made me wonder if fish sauce is related to MSG. Gemini confirms MSG is just salt and glutamic acid, which is to say fish sauce is naturally derived MSG. Fun story: I was riding a motorcycle across Vietnam a few years ago. Made some friends on an excursion, and we all went to dinner together. The restaurant was a little outdoor kitchen and some picnic benches in front of an apartment building…
You can find msg in your local grocery store, usually under the Accent brand. I've seen two pound jars of it in Costco.
I took pictures of empty 100 lb (45 kg) MSG containers in the trash outside Bao restaurant on St Marks in NYC