Glutamate is Excitotoxicity: because glutamate is absorbed very quickly in the gastrointestinal tract (unlike glutamic acid-containing proteins in foods), glutamate could spike blood plasma levels of glutamate. Glutamic acid is in a class of chemicals known as excitotoxins, high levels of which have been shown in animal studies to cause damage to areas of the brain unprotected by the blood–brain barrier and that a variety of chronic diseases can arise out of this neurotoxicity. There has been debate among scientists on the significance of these findings since the early 1970s, when John Olney found that high levels of glutamic acid caused damage to the brains of infant mice. The debate is complex and has focused mainly on whether the increase in plasma glutamate levels from typical ingestion levels of glutamate is enough to cause neurotoxicity and on whether humans are susceptible to the neurotoxicity from glutamic acid seen in some animal experiments.

At a meeting of the Society for Neuroscience in 1990, the delegates had a split opinion on the issues related to neurotoxic effects from excitotoxic amino acids found in some additives such as monosodium glutamate.

Some scientists believe that humans and other primates are not as susceptible to excitotoxins as rodents and therefore there is little concern with glutamic acid as a food additive. While they agree that the combined effects of all food-based excitotoxins should be considered, their measurements of the blood plasma levels of glutamic acid after ingestion of monosodium glutamate and aspartame demonstrate that there is not a cause for concern.

Olney, a longtime campaigner for greater regulation of MSG, believes that primates are susceptible to excitotoxic damage, and other studies have shown that humans concentrate excitotoxins in the blood more than other animals. Based on these findings, Olney claims that humans are approximately 5–6 times more susceptible to the effects of excitotoxins than rodents are. While he agrees that typical use of monosodium glutamate does not spike glutamic acid to extremely high levels in adults, he is particularly concerned with potential effects in infants and young children and the potential long-term neurodegenerative effects of small-to-moderate spikes on plasma excitotoxin levels.[ wiki]

The FDA does not require foods and ingredients that contain glutamate as an inherent component to be listed on a label. Two examples include yeast extracts and natural flavor. These ingredients are to be declared on the label by their common or usual names but not identified as glutamate, glutamic acid or monosodium glutamates. The term 'natural flavor' is now used by the food industry to refer to glutamic acid. Because of lack of regulation, it is impossible to determine what percentage of 'natural flavor' is actually glutamic acid.
The food additives disodium inosinate and disodium guanylate are usually used in synergy with monosodium glutamate-containing ingredients, and provide a likely indicator of the addition of glutamate to a product.[ wiki]