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Monosodium glutamate, more popularly known as "MSG," is a widely-used flavor additive known for its contribution to the fundamental flavor known as umami. It is also the subject of food woo purporting it to be dangerous.
What it is
MSG is a sodium salt of glutamate, which in turn is the carboxylate anion of glutamic acid, one of the twenty standard amino acids. Glutamic acid and its derivatives are essential to numerous functions in the body. As a standard amino acid, it is used to build proteins. Glutamate is a metabolic intermediate and neurotransmitter.
MSG and similar sodium salts have been widely used in Asian cuisine for centuries; they are produced during the fermentation of such ingredients as soy sauce, and are also found in certain seaweeds. Now produced synthetically or by bacterial fermentation, MSG is one of the most common flavorings used in Chinese, Japanese, and Cantonese cooking. Through this, use of MSG spread into Europe and the United States. MSG is also used extensively in Native American cuisine, and in the 16th century spread to Italy and Asia, in the form of the MSG-rich
fruit vegetable, the tomato. This is why if you aren't sure what to add to your recipe, you add tomatoes. No exceptions.
Other natural sources of glutamic acid include yeast (including that disgusting Marmite stuff), broccoli, wheat, meat, and Parmesan cheese. Glutamic acid can also be liberated from vegetable protein via acid hydrolysis; hydrolyzed soy protein is widely used as a food additive to improve flavor because it's a shelf-stable source of glutamic acid.
Health concernsIt became widely believed in the 1980s in the United States that MSG posed a health hazard, with a phenomenon called "Chinese Restaurant Syndrome" reportedly resulting from the additive. Evidence for harmful effects from MSG is almost entirely anecdotal. In response, the Food and Drug Administration reviewed the literature and studied the chemical, determining:
"There is no evidence in the available information on [substance] that demonstrates a hazard to the public when it is used at levels that are now current and in the manner now practiced. However, it is not possible to determine, without additional data, whether a significant increase in consumption would constitute a dietary hazard."
Though there are no large, reputable studies that show any reaction, and multiple studies demonstrate that there is no discernible syndrome except for people taking the placebo, public-consumption websites still note that "A small percentage of people may have short-term reactions to MSG." While MSG is not considered dangerous by the scientific community, its use in food preparation is seen in culinary circles as "cheating", improving the flavour of substandard foods in the same way as adding a lot of common salt to fast food.
One of the most common claims made by woo-peddlers is that MSG will give you seizures or cause brain damage or autism in some way because of the glutamate it contains. This is based on the fact that high levels of glutamate can cause excitotoxicity in the brain. This is true, but the problem with this claim is that glutamate does not cross the blood-brain barrier in healthy humans (though it is a possibility for those with some disease that weakens the barrier). Thus, unless you inject it past the blood-brain barrier directly into the brain, it will have no effect on brain activity.
Despite a widespread belief that MSG can elicit migraine headaches, there is no consistent clinical data to support this claim, nor is there evidence that some individuals are more sensitive to MSG than others.  It is more likely that migraines and the other alleged symptoms of "Chinese Food Syndrome" are caused by the high levels of salt, carbohydrates and oils in Americanized Chinese food.
- The Notorious MSG’s Unlikely Formula For Success (sadly, not about the Chinese-American hip-hop group "Notorious MSG")
- Skeptical Raptor's Blog: MSG-myth versus science
- Monosodium Glutamate, a Safety Assessment
- Hawkins, RA. The blood-brain barrier and glutamate. Am J Clin Nutr. 2009 Sep;90(3):867S-874S. Epub 2009 Jul 1.
- Jinap S., Hajeb P. Glutamate. Its applications in food and contribution to health. Appetite. 2010 Aug;55(1):1-10. Epub 2010 May 12.
- Williams AN, Woessner KM. Monosodium glutamate 'allergy': menace or myth? Clin Exp Allergy. 2009 May;39(5):640-6. Epub 2009 Apr 6.
- Freeman M. Reconsidering the effects of monosodium glutamate: a literature review. J Am Acad Nurse Pract. 2006 Oct;18(10):482-6.
- Geha RS, Beiser A, Ren C, Patterson R, Greenberger PA, Grammer LC, Ditto AM, Harris KE, Shaughnessy MA, Yarnold PR, Corren J, Saxon A. Review of alleged reaction to monosodium glutamate and outcome of a multicenter double-blind placebo-controlled study. J Nutr. 2000 Apr;130(4S Suppl):1058S-62S.
- Skeptical Raptor MSG-myth versus science