I've seen a few threads here and elsewhere promoting supplementation of glutamate in conjunction with nootropics, and I've also seen a few condemning it. However, I haven't seen a clear consensus, nor have I seen much evidence to back up either side of the debate. Perhaps we can get to the bottom of this.
First, a little introduction and specificity:
Glutamic acid is one of 20 directly encoded proteinogenic amino acids (the other two proteinogenic amino acids, selenocysteine and pyrrolysine, are incorporated into proteins by distinctive biosynthetic mechanisms). In the body, glutamic acid loses one hydrogen atom and becomes glutamate...although in general, this technicality is ignored and people (even scientists) use the terms "glutamate" and "glutamic acid" interchangeably. Nevertheless, it bears reminding that glutamate is not the same thing as glutamine. Incidentally, glutamate can be converted by the body to glutamine, and likewise glutamine can be converted to glutamate, but this does not imply that sufficient levels of one will guarantee sufficient levels of the other.
A quick look on Wikipedia will inform the reader that "Glutamate is an important neurotransmitter that plays a key role in long-term potentiation and is important for learning and memory." Couple that with the fact that several nootropics, including and perhaps most notably the racetams, increase the brain's use of glutamate, and thereby decrease brain glutamate levels. For example:
Piracetam decreases the glutamate content of the brains of mice - http://www.ncbi.nlm..../pubmed/1685614
Aniracetam increases cortical glutamate release - http://www.ncbi.nlm....d?term=11852174
Oxiracetam selectively increases the release of glutamate in the hippocampus - http://www.ncbi.nlm..../pubmed/1361044
It would seem that glutamate reserves are depleted by racetam use (and likely the use of other nootropics with similar mechanisms of action), and that glutamate supplementation may be desired in this case.
However, there have been concerns over glutamate excitotoxicity, which could cause neuronal damage and cell death, resulting in everything from stroke to epileptic seizures. This is the real crux of the matter, and what must be addressed.
Glutamate, as mentioned above, is essential to the body, and is present in sufficient levels in normal humans. A diet low in natural sources of glutamate results in symptoms such as insomnia, problems concentrating, and mental exhaustion. Total deficiency of glutamate would cause death, but it would be almost impossible to deplete this amino acid completely, as the body produces it from glutamine when it cannot acquire it dietarily.
The question becomes: If glutamate is important for nootropic users, how might one determine if he or she is deficient, and how might one supplement it without running the risk of excitotoxicity?
Although nothing comes to mind for determining deficiency other than trial and error (suggestions?), we can take a quick look at dietary sources of glutamate to see how much humans safely ingest every day.
If, for example, we drop by USDA's FNS web site, we see that the average serving of corn is about 90 grams: http://www.fns.usda...._F210_Final.pdf
If we take a look at USDA's NAL web site, we see that corn contains 0.636 grams of glutamate per 100 grams: http://ndb.nal.usda....ormat=Full&new=
Given the average 90 gram serving noted above, this means that humans regularly consume 0.5724 grams (or 572.4 milligrams) of glutamate via corn.
If you think that's significant, the next example blows it out of the water. The USDA recommends that at a bare minimum, adults consume at least 6 ounces of grains per day, 3 of which should be whole grains: http://www.ers.usda....48/err50_1_.pdf
However, the average healthy, active human far exceeds this recommendation. Per the USDA's NAL web site, the average slice of whole wheat bread weighs 28 grams, and is composed of 1.894 grams per 100 grams glutamate: http://ndb.nal.usda....ormat=Full&new=
This means that every time you eat a slice of whole wheat bread, you're ingesting 0.530 grams (or 530 milligrams) of glutamate. In general, people use two slices per sandwich, which amounts to 1.06 grams per sandwich, aside from any additional items containing glutamate.
Cracked wheat weighs about 25 grams per slice, and contains 2.770 grams per 100 grams glutamate: http://ndb.nal.usda....ormat=Full&new=
This means that for every cracked wheat sandwich you eat, you're ingesting 1.385 grams of glutamate.
Considering the fact that many very healthy people consume multiple sandwiches per day, and adding to that the fact that, for example, 12-inch subway sandwiches contain at least three times as much bread as normal sandwiches, people ingest many grams of glutamate per day via wheat bread alone.
Other natural dietary sources of glutamate include:
Eggs (for example, fried eggs, weighing on average 46 grams, contain 1.87 grams per 100 grams glutamate, or 860.2 milligrams glutamate per fried egg) - http://ndb.nal.usda....ormat=Full&new=
Peas (peas contains 0.741 grams per 100 grams glutamate - the average serving of peas, one cup or 145 grams, thus contains 1.07 grams of glutamate) - http://ndb.nal.usda....ormat=Full&new=
Parmesan Cheese (contains a whopping 8.696 grams per 100 grams glutamate - the average serving of one ounce or 28.35 grams thus contains 2.465 grams of glutamate) - http://ndb.nal.usda....ormat=Full&new=
...and the list goes on. Google the other twenty or so common dietary sources, and run them through the USDA NAL foods list here: http://ndb.nal.usda....ndb/search/list
All this points to the fact that, if one can easily skew glutamate ingestion by several grams just eating a subway sandwich, supplementing a gram or two isn't going to cause any significant harm. Moreover, if it's been conclusively established that the racetams deplete glutamate, taking a glutamate supplement while taking a racetam supplement would seem to be a very good idea. Alternately, you could just increase your dietary intake of glutamate, by eating more of the foods mentioned above (and others that contain significant amounts of glutamate).
Input?
Edited by LBGSHI, 03 January 2013 - 07:00 PM.