Glutamate (or glutamic acid) is an amino acid found in meat, tomatoes, and other foods. It is responsible for the “umami” taste. It is also found in a slightly different form as a neurotransmitter in the brain. The food additive monosodium glutamate (MSG), first used in Japan, is derived from fermented vegetables, and is indistinguishable from glutamate found in naturally-occurring proteins.
The brain maintains a low concentration of glutamate in the fluid surrounding its cells; the level in our bloodstream and in the rest of the body is much higher. This is possible because the brain is separated from the rest of the body by the blood-brain-barrier. For the most part, glutamate cannot cross this barrier unless it is actively transported by cells. So even if you ingest a lot of MSG with your food, it would be difficult for it to find its way into your brain! After some reports of people suffering from neurological symptoms after eating in certain restaurants, there has been a lot of research on the effects of MSG. When studies of MSG consumption are blind, meaning the researchers are unaware of which group ingested MSG while doing their analysis, there seems to be little difference between the two groups. The FDA has therefore classified it “generally considered as safe”.