IDENTIFICATION AND USE: a food additive that is used as a flavor enhancer primarily in Asian cooking although it is commonly found in many processed foods. MSG comes from glutamic acid that is naturally found in mushrooms, fermented soy products such as soy sauce and parmesan cheese. Glutamic acid is part of a large category of glutamates which ultimately make up the fifth taste category of umami.

HUMAN EXPOSURE AND TOXICITY: glutamate is absorbed from the gut by an active transport system specific for amino acids. This process is saturable, can be competitively inhibited, and is dependent on sodium ion concentration. During intestinal absorption, a large proportion of glutamic acid is transaminated and consequently alanine levels in portal blood are elevated. If large amounts of glutamate are ingested, portal glutamate levels increase. This elevation results in increased hepatic metabolism of glutamate, leading to release of glucose, lactate, glutamine, and other amino acids, into systemic circulation. The pharmacokinetics of glutamate depend on whether it is free or incorporated into protein, and on the presence of other food components.

Digestion of protein in the intestinal lumen and at the brush border produces a mixture of small peptides and amino acids; di-and tri-peptides may enter the absorptive cells where intracellular hydrolysis may occur, liberating further amino acids. Defects are known in both amino acid and peptide transport. Glutamic acid in dietary protein, together with endogenous protein secreted into the gut, is digested to free amino acids and small peptides, both of which are absorbed into mucosal cells where peptides are hydrolyzed to free amino acids and some of the glutamate is metabolized.

Excess glutamate and other amino acids appear in portal blood. As a consequence of the rapid metabolism of glutamate in intestinal mucosal cells and in the liver, systemic plasma levels are low, even after ingestion of large amounts of dietary protein.

ANIMAL STUDIES: according to Dr. Russell Blaylock, who wrote a book on the subject called Excitotoxins: The Taste That Kills, sensitivity to MSG builds up in our bodies until we reach what he calls our “threshold of sensitivity.” That’s because MSG overstimulates our nervous system — exciting our nerves and causing an inflammatory response. With time, these repetitive inflammatory responses cause our nerves to start producing more and more nerve cells that are sensitive to this kind of stimulation.

The more overly-sensitive nerve cells we have, the stronger our immediate response to MSG will be. Way back in 1957, a team researchers decided to see if glutamate could help repair a diseased retina. Remember, glutamate is a common and necessary amino acid in our diet (arguably the most common neurotransmitter in the brain), so this presupposition isn’t so far-fetched.

The researchers fed rats MSG and were shocked by their results. Rather than repairing the disease, the MSG destroyed the retinal cells that allow vision! A decade later, the neuroscientist Dr. John Olney used their method of destroying retinal cells so that he could study visual pathways to the brain. He found that MSG not only destroyed retinal vision cells, but also parts of the brain. This brain damage was done as neurons became over excited, virtually exciting themselves to death. He called this “excitotoxicity,” and that has led subsequent researchers to describe MSG as an “excitotoxin.” While the naturally occurring glutamates in food aren’t dangerous, processed free glutamic acids like MSG are. Not only do they cause brain damage and lead to nervous disorders, but they also cause radical hormone fluctuations. Mice injected with MSG become rapidly obese, inactive, and have other hormonal issues.

ADVERSE REACTIONS: can involve symptoms such as numbness, burning sensation, tingling, facial pressure or tightness, chest pain, headache, nausea, rapid heartbeat, drowsiness, and weakness. Asthmatics may experience these symptoms as well as difficulty in breathing.