Monosodium glutamate (MSG) is one of many salt forms of glutamic acid, which has unique flavour-enhancing qualities commonly used as a food additive.(1) The ‘MSG symptom complex’ otherwise known as the ‘Chinese restaurant syndrome’ (CRS) was termed by Robert Ho Man Kwok in 1968.(1-3) After dining at American-Chinese restaurants, Kwok experienced recurring symptoms of numbness, chest pain, nausea, and weakness.(2, 3) Kwok then wrote a letter to the editor of the New England Journal of Medicine describing these symptoms.(3) He hypothesised that these symptoms may have been attributed to the alcohol in Chinese cooking wine, salt, or MSG, thereby, coining the term ‘Chinese restaurant syndrome.’(5) Despite being classified as safe for consumption by the United States Food and Drug Administration, anecdotal allegations continue to rise, creating topical controversy over the safety of MSG.(4) Furthermore, a number of small, uncontrolled studies implying a variety of MSG-induced reactions have been published.(5-7)
The anecdotal claim made by Kwok sparked many studies on the effect of monosodium glutamate, many of which had flawed study-designs.(3, 4, 7-9) One of the earliest studies performed in 1969 found that almost all subjects tested had a dose-response reaction to MSG.(5) However, this study is plagued because the tests were not all blinded and there were only six subjects in the study.
Concerns about MSG fluctuated after a cross-sectional study concluded that 25% of the test population experienced CRS.(7) In this study, subjects were simply asked, ‘Do you think you get Chinese restaurant syndrome?’ and listed a description of potential symptoms. The study’s design and validity was flawed as it did not address causality, subjects’ recall bias, and demand bias; but suggested a correlation between symptoms and CRS based on subjects’ responses.(1, 7)
Another study that only included fourteen subjects hypothesised that ‘CRS was secondary to acetylcholinosis’ since both display similar symptoms of flushing and chest pain and, glutamate is converted to acetylcholine.(6) Accordingly, one test group was given MSG and another test group was given prophylactic atropine.(6) It was observed that subjects that received prophylactic atropine did not display CRS characteristics, thereby it was deduced that MSG was responsible for CRS symptoms.(6) Morselli and Garattini(8) took these preliminary findings(6) and expanded on it by conducting a double-blind, placebo-controlled crossover study. Subjects were administered 3g of MSG hidden in beef broth. Results revealed no significant differences in symptoms between the test and placebo groups, thus suggesting that results from the previous study by Ghadmi(6) are questionable.(8)
In 1993, Tarasoff and Kelly(9) constructed a more robust study design that increased randomization and decreased demand bias. Seventy-one fasting subjects were recruited to consume 5g of MSG post consumption of a standardised breakfast.(9) Following, subjects were asked open ended questions such as; ‘did you taste anything unusual after breakfast?’ For both the test and placebo groups, the most common response was ‘nothing’.(9) Interestingly, one self-claimed MSG-sensitive subject reported a strong reaction to the placebo and not to the MSG.(9) Subsequent studies have likewise failed to find conclusive evidence to support the proposed association between MSG and CRS.(10)
Monosodium glutamate is responsible for the Chinese Restaurant Syndrome: FACT or FICTION? -FICTION-
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3. Kwok RHM. Chinese-restaurant syndrome [letter]. N Engl J Med 1968;278:796.
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