“The most prominent symptoms are numbness at the back of the neck, gradually radiating to both arms and the back, general weakness and palpitation.”
This terrifying set of symptoms sounds like a heart attack, but is actually the description of the ailments of “Chinese Restaurant Syndrome” as described by Dr. Robert Ho Man Kwok in a letter to the editor for the New England Journal of Medicine. Dr. Kwok claimed that he would consistently experience this syndrome after consuming Northern Chinese fare with his colleagues. In the letter, he attributed these symptoms to one of three possible culprits: cooking wine, excess levels of salt, or monosodium glutamate (MSG) used in the food. A number of individuals soon followed with similar letters affirming that they too had experienced this set of symptoms. As MSG is the only ingredient that differentiates Chinese food from other restaurant cuisines, MSG became the sole antagonist for this so-called Chinese Restaurant Syndrome. And thus MSG became enemy #1 overnight after a single a non-expert letter to the editor.
MSG is used as an ingredient to elicit the savory flavor, or umami taste, in foods. As the newest addition to the basic tastes, umami is less recognizable than sweet or salty. Our perception of umami is generally attributed to our evolutionary roots. Amino acids, the building blocks of proteins, elicit the flavor of umami which could have signaled to our early ancestors that a specific food was a good source of protein. Glutamic acid is a specific amino acid that triggers umami taste. Adding a sodium molecule to glutamic acid yields the compound we know as monosodium glutamate, or MSG.
Much of the research around umami and MSG is from Japan. Soups are often prepared with seaweed in Japanese cuisine to deliver a unique savory flavor. In the early 20th century, salts of glutamic acid like MSG were isolated in natural soup preparations that use seaweed as an ingredient, revealing that MSG was a primary source of that desirable flavor. While the idea to add pure MSG as an ingredient to foods in order to increase the perception of savory came much later, the practice of adding MSG-containing ingredients has been around for a long time. For example, breaking down or hydrolyzing proteins using heat or aging processes like fermentation creates these free amino acids which elicit umami taste. That’s why hydrolyzed vegetable protein or hydrolyzed yeast extract (hello, Marmite and Vegemite!) are such popular ingredients around the world. Ask any chef, and they’ll tell you that the ideal dish is one that balances the five basic tastes creating a deeper and more lasting flavor profile.
MSG has been a gras (generally recognized as safe) food ingredient since 1958 by the FDA, and the Codex Alimentarius categorizes glutamate and all of its various salts as flavor enhancers. However, after the Chinese Restaurant Syndrome came on the scene, MSG became hotly contested as an additive that causes adverse effects like migraines and asthma. In response to this public outcry, a comprehensive safety review was conducted on MSG and other umami-inducing salts in 1987 by the Joint FAO/WHO Expert Committee on Food Additives. They concluded that MSG does not pose a health risk. In fact, they did not deem it necessary to specify a daily intake level as the quantity of glutamate to cause acute toxicity was so high. This was later confirmed in another evaluation in 1991 by the Scientific Committee for Food of the Commission of the European Communities.
On average, Americans consume approximately 0.55 g/day of added glutamate in foods which is similar to the daily consumption in the UK. Compare that to the average Asian consumer who ingests 1.2-1.7 g/day of added glutamate. Additionally, it has been shown time and time again that the human body metabolizes all forms of glutamate the same way—added or naturally-occurring. In fact, contrary to popular thought, glutamate levels in the blood do not increase after foods with high levels of added glutamate are ingested.
In general, there is weak evidence, at best, that links MSG to Chinese Restaurant Syndrome symptoms. In the most comprehensive study to date, a collaborative research project between Boston University, Harvard University, Northwestern University, and the University of California at Los Angeles investigated the effects of glutamate on self-reported MSG-sensitive subjects. Out of the 130 subjects included in the testing, only two had consistent responses to glutamate samples in a double-blind, placebo-controlled, randomized trial. Furthermore, the symptoms themselves were not reproducible among the glutamate-containing samples. This was not a statistically significant response, and keep in mind that these are self-reported sufferers of Chinese Restaurant Syndrome effects. The researchers concluded that glutamate does not cause reproducible sensitivities reported by some consumers.
In addition to general sensitivity, there have been several specific symptoms “linked” with MSG including hives/swelling, asthma, stuffy nose, and headaches/migranes. The research addressing each of these is outlined below:
Hives/ Swelling (urticaria/ angio-oedema) – Many studies that investigate the link between MSG and these allergic skin reactions are difficult to interpret because subjects are used that are prone to allergic reactions, and they are often asked to refrain from taking any antihistamines during the testing period. This confounds the results because it makes it almost impossible to ascertain what is causing rash-like symptoms. In a study that asked subjects to reduce the antihistamine use to the lowest levels possible, there was no reproducible link between skin swelling and MSG consumption during double-blinded trial. There have been single cases (two) where urticaria and angio-oedema can be caused by MSG ingestion, though this is extremely rare.
Asthma – Similar to the hives studies, asthma studies are convoluted because subjects are used that report asthmatic symptoms to Chinese foods, and those subjects are asked to refrain from asthma medication. It is difficult to separate effects from the consumption of glutamate or withdrawal from preventative attack medication. Furthermore, the results within studies and between studies have not been reproduced in subjects, and it has been reported that no long-term health effects exist in epidemiological studies. There is no consistent evidence that glutamate ingredients trigger asthma symptoms.
Stuffy nose (rhinitis) – There are very few studies in this area, but a weak link has been established between MSG ingestion and rhinitis in three patients. These results have not been repeated; therefore, not enough research has been conducted to make scientifically-informed conclusions.
Headaches/ Migraines – It is hypothesized that glutamate may interfere with acetylcholine synthesis which may be the cause of reported migraines upon consumption of foods with added glutamate. However, there have been zero clinical trials to date testing glutamate and migraine/headache symptoms specifically, so there is no in vivo evidence linking the two.
The crisis of Chinese Restaurant Syndrome wreaked havoc on the food and restaurant industries simply by the submission of one infamous letter to the editor in 1968. Immediately MSG began to be phased out, where possible, from food products which spurred research and systematic reviews of glutamate food additives. As a result of that heightened research, there is no significant evidence for harm from glutamate except in an extremely small subset of the population. In fact, research in the area has highlighted positive effects from MSG including its role in several facets of digestion and reduction of sodium in foods at levels up to 30-40%.
In a time of hypersensitivity toward food additives, the story surrounding MSG’s stigma should be a cautionary tale to not rush to judgment before banning certain ingredients from your diet. Always read articles (including this one) from a critical point of view. And look to the scientific literature rather than an opinion on the safety of a particular food ingredient.
Kelsey is originally from Minnesota and received her B.S. in Food Science from Purdue University. Most recently, she attained an M.S. in Food Science from Penn State where her research focused on mitigating the taste of bitter for pediatric medications. She lives in New York as a confectionery technologist (candy product development = dream job!). Kelsey loves eating cookie dough by the spoonful, collecting cookbooks, and watching old episodes of Top Chef. You can follow along with her adventures in the kitchen on her blog Appeasing a Food Geek! (Follow her on Twitter! @Kelsey_Tenney)