After 210 years of kitchen use, authorities have yet to find hardcore evidence that warrants the banning of MSG. Glutamates (the main component in MSG) are not at all foreign or invasive to the human body.
Glutamates naturally present in food. Concentrations are very high in tomato sauces and pastes, sharp cheeses like Parmesan, black beans, kelp, seaweed, dried mushrooms, Vegemite, Marmite, fish sauce, soy sauce, oyster sauce, foods containing added Hydrolyzed Vegetable Protein (HVP), stocks cubes and concentrates, and more. Note that the body processes free (natural) glutamates and MSG the same way.
Glutamates in the body are mostly resident in the human brain, which releases these neurotransmitters. Glutamates are responsible for sending signals between nerve cells. Glutamates aid learning and memory. That may very well be the reason why Glutamate Toxicity can result in headaches and even brain cell damage after a stroke.
MSG is extracted and crystallized glutamates + sodium, the process was discovered by Japanese Professor Ikeda in 1908. He was the first to commercially produce and sell it under his personal brand "Ajinomoto". MSG is considered an essential ingredient in Asian Cuisine. It is a unique flavour enhancer and no other spice or herb can produce what MSG brings out in dishes.
Nowadays, MSG undergoes fermentation procedures rather than extraction and crystallization. Food regulatory boards officially classify MSG as GRAS or Generally Regarded As Safe with labeling requirements, meaning, products must disclose MSG content. While natural glutamates need not be labelled, products that use ingredients containing natural glutamates cannot be labelled as MSG-free or "No Added MSG".
For safety, consume MSG-added foods minimally so you can avoid what is called the "Chinese Restaurant Syndrome". It is a condition some people experience after eating Chinese food or dishes containing MSG. The symptoms are headache, nausea sometimes numbness and vomiting. Headache Australia further adds "pressure and tightness in the face, burning over the trunk, neck and shoulders; pressing pain in the chest" which can come within 20 minutes of having Chinese food. The site further informs that sensitive individuals may experience the syndrome upon consuming 3g of MSG, an amount found in 200ml of wonton soup.
If you have personally experienced symptoms like these, you may fare better by avoiding food containing MSG. Remember to check labels when buying products and inquire about MSG in the food you are about to order in a restaurant.
Cooking Tip: For substitute flavour enhancers, try adding parmesan, a little Vegemite, or a little sugar to the pot when you're almost done cooking.
More about MSG:
If MSG is so bad for you, why doesn't everyone in Asia have a headache? (The Guardian)
Is MSG as Bad as It's Made Out to BE? (BBC)
Why MSG Allergy is Fake Science (Chinese Restaurant Syndrome Myth) (The Guardian)
What is MSG? (HuffPost)
What is MSG? (HuffPost)