Monosodium Glutamate (MSG) is a health concern because it contains glutamate. Glutamate is the salt form of "Free Glutamic Acid" - a toxin that is associated with serious health problems such as digestive distress, heart attacks, Fibromyalgia, behavior problems, insulin resistance, weight gain, and a long list of other symptoms. [1, 2, 3, 4]
Due to insufficient labeling laws, food companies use many hidden names to disguise Free Glutamic Acid in their ingredients lists. So consumers must look for more than just "MSG" on food labels.
To understand why processed Free Glutamic Acid is associated with so many health problems, it is helpful to learn about natural Glutamic Acid - an amino acid (a building block of protein) that occurs naturally in the body as one of many excitatory neurotransmitters (chemicals that "excite" cells into action).
Glutamatic Acid also occurs naturally in certain unprocessed, whole foods (e.g., tomatoes). In this natural form, it is bound (i.e., linked) together with other amino acids to form a protein. Once ingested, the protein is broken down slowly by the digestive system. The Glutamic Acid is released gradually into the blood stream and is non-toxic. If one ingests more than the body needs, the cells clear away the excess just as they were designed to do. The digestion of these natural, whole food sources releases such a small amount of Glutamic Acid that even people who react to processed MSG can usually tolerate them.
When food manufacturers break down a protein (usually from corn, soy or wheat) to make processed Free Glutamic Acid, they "free" the glutamic acid from the links that bind it to other amino acids in nature. When one ingests this already-broken-down, free form of Glutamic Acid, blood levels of glutamate can spike to more than 20 times the usual amount because the digestive system does not have to work to break down the links. The human nervous system is not equipped to handle such quickly-absorbed doses. The excess glutamate cannot be efficiently cleared away, so it accumulates around the cells throughout the body, over-exciting them to the point of damage or death.
This disruption at the cellular level leads to a range of physiological reactions that may be as minor as a runny nose or as life-threatening as a heart attack. According to experts like Dr. Russell Blaylock, M.D., Free Glutamic Acid is a toxin, not an allergen. Some people are sensitive to lower dosages than others, but it affects everyone to some degree. 
There is often a delay between ingestion and onset of symptoms, preventing many people from realizing the connection. Most acute symptoms will display within 48 hours (many within 30 minutes) of ingestion, but some health effects (e.g., obesity, infertility) have been demonstrated in lab mice long after exposure.
Because glutamate receptors line various organs and tissues (brain, heart, lungs, reproductive organs, digestive tract, etc.) throughout the body, ingesting processed Free Glutamic Acid can disrupt just about any system and cause a wide variety of symptoms. Luckily, much of this damage is reversible, and many sufferers resolve their symptoms (often within 7-10 days) by completely eliminating Free Glutamic Acid from their diets. 
Are you wondering if you would notice any difference by eliminating toxic ingredients from your diet? Why not challenge yourself to make some changes! Start by skipping the drive-thru and preparing a meal at home from basic, whole food ingredients. Begin to minimize your reliance on processed food, and learn to thoroughly review every ingredient list to be sure that you are not ingesting any of these hidden forms of MSG. It takes more time and effort, of course, but you're worth it!
- Anglesey, D. Battling the MSG Myth: A Survival Guide and Cookbook. Kennewick: Front Porch Productions, 1997.
- Blaylock, R.L. Excitotoxins: The Taste that Kills. Santa Fe: Health Press, 1997
- Erb, J.E. and T.M. The Slow Poisoning of America. Virginia Beach: Paladins Press, 2003.
- Schwartz, G.R. In Bad Taste: The MSG Symptom Complex (revised). Santa Fe: Health Press, 1999.
Christy Pooschke is the author of Eating Additive-Free: A Natural Cookbook & Grocery Shopping Guide, and she teaches people how to prepare natural, additive-free foods through her website at GroceryGeek.com. Christy's passion for natural health was sparked in 2007 when she eliminated her Fibromyalgia symptoms through natural diet and lifestyle changes. Christy also operates CompletelyNourished.com - an online community for folks interested in real food and natural living. Join today!