MSG is actually a form of glutamic acid, with sodium, and sodium is sodium, wherever it occurs. Is MSG all that bad for you? What foods contain it?
MSG or monosodium glutamate is associated with the "fifth" taste, the savory or umami taste ("umami" means delicious, in Japanese; similarly the Fulani [Niger-Congo] word nyami means "delicious" or "eat").The other four tastes are salty, sweet, bitter, and sour. The "umami" taste supposedly actually enhances the other four.
Originally made from seaweed, MSG occurs naturally in seaweed. It "was discovered when a kelp broth was evaporated," according to "3 Fat Chicks." Today MSG is manufactured rather than derived from seaweed. MSG was initially manufactured using hydrochloric acid and at one point was made from wheat gluten. Today it's gluten-free. It is usually fermented from starch or foods with sugar (beets, sugar cane) using bacteria. So what is all the hype?
Monsodium glutamate is actually a glutamate where sodium is the component with the glutamic acid. It's also known as l-glutamate (not l-glutamine, which however is related; see below).
Glutamate, Glutamic Acid, and Sodium
Glutamates and glutamic acid are not quite the same of course. MSG is the former. Glutamates are glutamic acids that have been "combined with a positively charged molecule" (such as sodium, in monosodium glutamate) according to Livestrong.org. L-glutamine is a glutamic acid, not a glutamate (although it converts to one in the body).
L-glutamine is actually an amino acid, and it's found in 60% of body mass. Proteins in the body require l-glutamine and l-glutamine is needed for muscle tissue growth. It's thus a popular supplement for body builders, and one time intake is considered safe. (But it's probably a good idea to combine l-glutamine with exercise and to limit intake.)
L-glutamine contains no sodium, so can be ingested by people on a sodium-restricted diet. MSG on the other hand contains sodium. The amount of sodium in foods with MSG that you ingest should not exceed your dietary allowance of sodium. That is, no more sodium in MSG is tolerated than sodium in other compounds. However the amount of sodium in the MSG used to flavor a dish will generally be lower than the salt the MSG replaces, by up to forty percent, according to fitday.com, apparently because, with MSG's "umami" taste, all that salt is not needed.
Alas, many store-bought foods, with or without MSG, contain higher amounts of sodium than are appropriate for a single meal or snack (store-bought soups for example, unless sodium-free, may contain from 20 to 50 percent of the MDR in a single serving; some brands however keep sodium down to 12 to 18 percent of the MDR per serving).
Sodium Compounds: Toxicity
Still not all sodium compounds are the same. Perhaps one of the more dangerous of the sodium combinations is sodium benzoate, which is used as a preservative in soda pop (Coca Cola however is phasing out sodium benzoate). Sodium benzoate is also used to preserve the longevity of some other foods, for example, some brands of pre-prepared hommus-bi-tahini. Sodium benzoate is toxic until it's converted by the liver to harmless hippuric acid (with the help of the amino acid glycine) according to the World Health Organization (2000). And it's not always converted completely.
MSG: Over-stimulation of Neurons
MSG is not considered as toxic as sodium benzoate, although some individuals may find it to be so. Like other glutamates however (note again that l-glutamine converts to glutamate in the body), MSG consumption is associated with production of excitatory neurotransmitters, and, if it's not converted to glutamate by the body, perhaps also with gastric distress ("Chinese restaurant syndrome"). Because of its effect on blood vessels, it may also be associated with headaches.
Sodium, Other Electrolytes, and Health
Regardless of how much sodium you consume, it's always safer to balance other electrolytes (calcium, magnesium, and potassium) with the sodium, in order to reduce hypertension, and also because the heart and kidneys are sodium-potassium pumps. Indeed the muscles don't work properly without sodium (extracellular fluid) and potassium (intracellular fluid) in balance, and the body's electrolytes must be in balance for electrolytes to be properly absorbed. Normally the kidneys balance the electrolytes naturally, so long as all electrolytes (calcium, magnesium, potassium, sodium) are included in the diet, but illness or age can reduce kidney function. Seaweed and sea salt tend to contain electrolytes in balanced form although some varieties of the former may contain excessive iodine. Although originally made from seaweed, MSG does not contain the other electrolytes.
MSG and Blood Pressure
MSG Truth.org and some other groups, in any case, argue that MSG is pretty toxic, akin perhaps to sodium benzoate. One problem with MSG according to MSG Truth.org, is that it is a calcium channel opener. MSG Truth.org argues that it is not sodium intake that causes a rise in blood pressure, but rather the intake of calcium channel openers such as MSG.
According to information at food renegade.com, the word "spices" may be used to hide MSG in foods; but the inclusion of MSG under the umbrella term "spices" is no longer permitted in the U.S. However, according to Truth-In-Labeling, MSG may be identified as one of the ingredients in food using other "umbrella" terms, including "hydrolyzed vegetable protein, autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts, and protein isolate." It's found in seasoning and soup mixes, canned soups, and soy sauces, among other foods.
"Oriental" Food and MSG
Some Asian food preparations, including koji which is used to ferment foods, and the fermented grain used to make many foods (including miso), may increase glutamic acid but not glutamate in foods. According to "Koji Magic" (Foodie Traveler) this is especially true when chicken is fermented in a preparation such as shio-koji. The chicken, says Foodie Traveler, is high in protease, which has a role in the production of glutamic acid, which is just wonderful according to the author.
Also, some miso is made using "high speed" techniques, with mosodium glutamate used in making it. Thus miso made using high-speed preparation may contain monosodium glutamate.