I have gathered some additional information for you. As indicated in
the excerpt I posted above, studies show that dietary intake of
monosodium glutamate does not increase glutamate levels in the human
brain unless the MSG is taken in an amount so massive as to disrupt
the blood-brain barrier (what amount this might be is uncertain; even
doses of MSG thousands of times larger than the usual dietary serving
have not had this effect in test subjects).
Below I have reposted the previous link, plus some extra material.
"The macromolecule that transports acidic amino acids such as
glutamate and aspartate across the blood-brain barrier is
unidirectional and secretes these compounds from the brain into the
blood by an active transport mechanism (Pardridge, 1977). Hence,
administration of even an enormous dose of monosodium glutamate will
not affect brain glutamate levels unless it elevates plasma osmolarity
to the point of disrupting the blood-brain barrier."
National Academies Press: Effects of Nutrients on Neurotransmitter Release
http://books.nap.edu/books/030905088X/html/239.html
"Concerns were raised in the late 1960s by John Olney, M.D., of
Washington University, that high doses of MSG may adversely affect
brain function. Dr. Olney examined the possibility of MSG-induced
brain lesions through injection or force-feeding methods in rodents.
In one study, Olney subcutaneously injected neonatal mice, ages 2 to 9
days old, with single dosages of MSG. The amount of MSG injected
varied from 0.5 mg/g to even larger dosages of 4 mg/g of the neonate's
body weight, inducing brain lesions and a variety of other
physiological effects in the rodents.
However, the dosages of MSG used in these studies were extremely high
and the methods of injection, as well as force-feeding, do not
accurately represent the way humans consume MSG. Interestingly,
Olney's results could not be duplicated when large amounts were
administered in the diet.
Indeed, studies evaluating the normal dietary ingestion of MSG in
food, including amounts exceeding 40 g/kg body weight (5,000 times
higher than normal amounts ingested), found no harmful effects on the
brain."
IFIC Review on Monosodium Glutamate: Examining the Myths
http://www.geocities.com/HotSprings/2455/ir-msg.html
Here is an excerpt from a report on a study in which human test
subjects were given large doses of monosodium glutamate. Although
blood (plasma) levels of MSG rose, there were no reported changes in
behavior and no notable neurological effects:
"Fasting male subjects received each of four treatments on different
days: a large oral dose of monosodium L-glutamate (MSG; 12.7 g), the
MSG vehicle, an iv injection of TRH, or a high protein meal. Blood
samples were drawn via an indwelling venous line before and at 20-min
intervals after each treatment for 4 h. Plasma glutamate levels rose
11-fold within 1 h of MSG ingestion, but did not change appreciably
with any of the other treatments. Plasma PRL levels rose lo-fold after
TRH infusion and a-fold after the protein meal, but did not rise
significantly after MSG ingestion. No effects resulted from any of the
treatments on plasma LH, FSH, testosterone, GH, or cortisol
concentrations. Plasma levels of TSH, T,, and T, showed minimal
changes after any of the treatments except TRH; TRH elevated plasma
TSH and T, levels. Self-rating instruments of mood and side-effects
revealed no treatment-related effects on mood or physical state for up
to 48 h after each treatment. Together, these results suggest that
acute pharmacological elevations of plasma glutamate levels in adult
men produce minimal, if any, effects on hypothalamic or pituitary
function...
Because of the large size of the MSG dose employed in this study, we
wondered whether any side-effects might occur that have previously
been reputed to accompany MSG ingestion. We, therefore, administered
two standard self-reporting instruments before, during, and after each
treatment. One of these instruments focuses on behavioral changes, the
other on side-effects. Despite the enormous MSG dose (-160 mg/kg) and
the high plasma GLU concentrations that followed its ingestion, no
mood or other behavioral effects were reported by the subjects.
Moreover, no side-effects were reported, particularly those that have
previously been suggested to occur with MSG ingestion (e.g. headache,
dizziness, stiffness, weakness, chest pain, and nausea)"
Journal of Clinical Endocrinology and Metabolism: Short-Term
Neuroendocrine Effects of a Large Oral Dose of Monosodium Glutamate in
Fasting Male Subjects
http://jcem.endojournals.org/cgi/reprint/81/1/184.pdf
My Google search stragegy:
Google Web Search: "monosodium glutamate" neurotransmitter OR neurotransmitters
://www.google.com/search?hl=en&q=%22monosodium+glutamate%22+neurotransmitter+OR+neurotransmitters
Google Scholar Search: "monosodium glutamate" neurotransmitter OR neurotransmitters
http://scholar.google.com/scholar?q=%22monosodium+glutamate%22+neurotransmitter+OR+neurotransmitters&ie=UTF-8&oe=UTF-8&hl=en
I hope this is helpful. If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.
Best regards,
pinkfreud |
