MSG symptom complex is the name given by the U.S. Food and Drug Administration (FDA) to a collection of symptoms attributed since the late 1960s to consumption of a food additive called monosodium glutamate (MSG). Monosodium glutamate, the sodium salt of glutamic acid, is used as a flavor enhancer. It is known by a variety of chemical names, including glutamic acid, monosodium salt; monosodium glutamate monohydrate; sodium glutamate monohydrate; and monosodium L-glutamate monohydrate. Because the use of commercially produced MSG as a flavor enhancer began in Japan and China in the early twentieth century, MSG symptom complex was initially termed “Chinese restaurant syndrome” or CRS in the United States when it was first reported in 1968.
Reliable information about MSG symptom complex is difficult to come by for several reasons. First, initial reports were anecdotal, based on individual accounts of headaches, sweating, and nausea after eating food served in Chinese-American restaurants. Second, attempts on the part of medical researchers in multiple locations to reproduce the symptoms of the complex by administering pure MSG to human subjects in the absence of food failed to find evidence that MSG causes the symptoms of CRS. Other studies reported that no symptoms of CRS occurred in the subjects when they were given MSG together with food. Further studies carried out in the late 1990s indicated that, at most, only a small percentage of humans have short-term reactions to MSG in prepared foods. The symptoms that do occur are brief and end after a few hours.
MSG symptom complex was originally described as “numbness at the back of the neck, gradually radiating to both arms and the back” and “general weakness and palpitation.” More commonly, people who considered themselves sensitive to MSG reported symptoms that included nausea, headaches, flushing, drowsiness, or sweating.
Glutamic acid and glutamates are also involved in the human perception of flavor, and it is here that they entered the history of human food production and storage. Glutamic acid and glutamates are found naturally in tomatoes and in many fermented or aged foods such as cheese, soy sauce, fermented bean paste, and yeast extract. Glutamates are responsible for humans' perception of a taste called umami, or savoriness and meatiness, in addition to the wellknown tastes of sweetness, sourness, bitterness, and saltiness. Umami is a Japanese word coined by Kikunae Ikeda (1864–1936), a Japanese professor of chemistry. He derived umami from umai, the Japanese word for delicious.
Ikeda was curious about the cause of this distinctive sensation of taste. He isolated glutamic acid in 1908 from Laminaria japonica, a species of seaweed used in Japan to make a savory broth. Ikeda then found that monosodium glutamate, the sodium salt of glutamic acid, was not only a source of the umami taste but also the most stable glutamate and the easiest to form into crystals. In 1909, a Japanese company began to produce MSG as a flavor enhancer for use in ordinary kitchens. The product was called Aji-no-moto, which means “essence of taste” in Japanese. Although MSG was originally manufactured by breaking down vegetable proteins with hydrochloric acid, it has been produced since 1973 by bacterial fermentation of sugar beets, starch, or molasses. Used in Japan for decades before World War II, MSG entered American kitchens after the war in the form of Accent, a powdered form of monosodium glutamate sold by a company in New Jersey; and Sazón, a seasoning containing MSG for use in Mexican dishes and other types of Latin American cuisine.
MSG did not become controversial until 1968, when a Chinese-American physician named Robert Ho Man Kwok wrote a letter to the editor of the New England Journal of Medicine in which he claimed that eating in Chinese restaurants resulted in unpleasant symptoms that began within minutes of eating, including heart palpitations and numbness that began at the back of the neck and radiated to the upper arms and back. After publishing Kwok's letter, the journal received anecdotal reports from other readers, some of whom reported the same symptoms as Kwok, whereas others claimed to experience chills, facial flushing, or dizziness. Editors of the journal coined the term “Chinese restaurant syndrome” (CRS) and identified MSG as the likely cause.
In the following years, various groups of researchers attempted to prove either that MSG caused CRS as a short-term consequence of eating food containing it, or that the flavor enhancer had previously unknown long-term consequences for human health. None of these studies were able to demonstrate conclusively that MSG causes symptoms in more than a small subset of human subjects, and some of the study results could not be replicated by other researchers. Because the FDA had classified MSG as a generally recognized as safe (GRAS) food additive since 1959, it was sufficiently concerned about individual reports of Chinese restaurant syndrome that it requested the Federation of American Societies for Experimental Biology (FASEB) to conduct additional experiments regarding the safety of MSG. FASEB published a report in 1995 indicating that MSG is safe. A small number of subjects reported minor symptoms when they consumed 3 grams (about 3/4 of a teaspoon) of MSG without food. As a typical serving of food seasoned with MSG contains less than half a gram of MSG, the FASEB scientists concluded that the flavor enhancer is safe for use in cooking. Because of the controversy, however, the FDA presently requires foods that contain added MSG to identify the additive on the package label as monosodium glutamate. The agency does not, however, mandate that MSG be identified as an ingredient in tomatoes, cheeses, or other foods that naturally contain it.
MSG is considered safe by food standards regulators in the European Union, Australia, and New Zealand. EU regulations stipulate that MSG added to food must be identified as a flavor enhancer with the code number E621. The Australia and New Zealand Food Standards Code requires foods containing added monosodium glutamate to be labeled with “flavour enhancer” followed by the chemical name of MSG and the international numbering system (INS) number, 621.
As of 2018, there are no known risk factors for sensitivity to MSG.
Symptoms that have been associated with MSG symptom complex include:
There are no diagnostic tests for MSG symptom complex as of 2018.
The symptoms of MSG symptom complex resolve within a few hours after a meal without the need for specific treatment.
MSG is not considered a significant dietetic concern as of 2018; no reference is made to it on the Academy of Nutrition and Dietetics website, and no research studies have been done since 2011 on the additive as a cause of CRS. As noted, monosodium glutamate occurs naturally in such foods as tomatoes and cheese, and the amount needed to cause seizures in laboratory rats is about 3.1 teaspoons per 2.2 pounds of body weight (15800 mg/kg). Thus the amount of MSG required to have the same effect on the nervous system of an average adult human would be hundreds of times greater than the amount added to food to enhance its flavor.
Twenty studies of MSG had been registered with the National Institutes of Health as of 2018 regarding the additive's relationship to umami as a distinctive taste and its possible effect on appetite. Some researchers are investigating whether human enjoyment of the taste of umami increases food consumption and possibly contributes to obesity in developed countries.
No cases have occurred to date of people anywhere in the world becoming severely ill as a result of ingesting MSG in the quantities ordinarily found in prepared foods or taking large doses of pure MSG in the absence of food. Anecdotal reports indicate that people who do experience some of the symptoms of CRS usually feel normal within two hours after eating food containing it.
People who are concerned that they may be sensitive to monosodium glutamate should avoid the use of Accent or similar products; check food packaging labels for MSG on the list of contents; and eat only in restaurants that advertise that their food has no added MSG.
See also Food allergies ; Food sensitivities ; Sodium .
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Federation of American Societies for Experimental Biology (FASEB), 9650 Rockville Pike, Bethesda, MD, 20814, (301) 634-7000, (800) 43-FASEB, email@example.com, http://www.faseb.org .
Institute of Food Technologists (IFT), 525 W. Van Buren, Ste. 1000, Chicago, IL, 60607, (312) 782-8424, (800) 438-3663, Fax: (312) 782-8348, firstname.lastname@example.org, https://www.ift.org/ .
Office of Food Additive Safety, Center for Food Safety and Applied Nutrition, Food and Drug Administration, CPK-2 Building, Room 3044, 4300 River Road, College Park, MD, United States, 20740, (240) 402-1200, Fax: (301) 436- 2972
U.S. Food and Drug Administration (FDA), 10903 New Hampshire Ave., Silver Spring, MD, 20993, (888) 463-6332, https://www.fda.gov/AboutFDA/ContactFDA/default.htm , https://www.fda.gov .
Rebecca J. Frey, PhD