Monosodium glutamate (MSG) gained notoriety when it was first associated with "Chinese Restaurant Syndrome": a combination of headache, dizziness and other symptoms that some people experience after eating at a Chinese restaurant. MSG is frequently added to Chinese food, soups, seasonings, processed vegetarian foods and other items, both in restaurants and in store-bought processed foods. Controversy continues about the health effects of consuming MSG.
Chemical Structure
MSG is the salt of glutamic acid, an amino acid, created when glutamate combines with a single sodium atom. In some unprocessed foods such as tomatoes and mushrooms, the amino acid L-glutamic acid occurs naturally, but in those cases is bound to other amino acids. Thus MSG is also sometimes referred to as free glutamic acid. It contains both L- and D-glutamic acid, which are molecular mirror images of each other. Typically MSG contains 78 percent processed free glutamic acid and 22 percent salt along with some water.
Production
In the early 1900s a Japanese professor first identified glutamate as the constituent of konbu kelp that provided a "savory" flavor to foods. He then produced and patented MSG. MSG is now produced primarily from sugar beets, corn or sugar cane using either a fermentation process or vegetable protein hydrolysis--heating protein in the presence of an acid. Some bacteria can also convert carbohydrates into a precursor of MSG. MSG is sold by itself and included as an ingredient in many processed foods.
Sources
Some processed foods contain added MSG, which is listed on the label, while others have ingredients that themselves contain MSG. These ingredients include autolyzed yeast extract, hydrolyzed soy protein, sodium caseinate, calcium caseinate, maltodextrin, hydrolyzed lecithin, and often the ambiguous "natural flavoring." The Food and Drug Administration (FDA) does not require that companies disclose the presence of MSG in these other ingredients on food labels. According to TruthInLabeling.org, some ingredients when combined during processing can also create MSG, but disclosure of this fact is also not required.
Controversy
The FDA lists MSG as a "GRAS" substance, meaning it is generally recognized as safe. Research in recent decades varies in its results, with some studies indicating no harmful consequences of MSG consumption, and others showing that MSG does cause health problems. Natural health proponents continue to advocate removal of MSG from foods or at least stricter labeling standards, pointing both to the subset of people who are highly sensitive to MSG and to the general health impact of MSG consumption. Meanwhile the glutamate industry continues its claims that MSG is safe in typically consumed amounts, and points out that MSG is usually consumed in smaller amounts than is glutamate that occurs in food naturally.
Effect on the Body
According to MSGTruth.com, a specific subset of taste buds detect MSG and treat it as a signal of nutritional protein content in food, which can lead to increased consumption of MSG-containing food. MSG can also stimulate production of insulin from the pancreas even in the absence of carbohydrates, producing a decrease in blood sugar and increased hunger. A study in China, reported in the August 2008 edition of the journal "Obesity," showed increased rates of obesity in individuals using MSG. The Glutamate Association suggests that consumers can reduce their sodium intake in food by using small amounts of MSG, and notes that the FDA has concluded that MSG does not differ from glutamate found naturally in foods.
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