I found this answer Dr Mike Eades gave to a question on his MSG article:
Mike, have you read Excitotoxins: The Taste that Kills by Russell Blaylock?
His credentials seem solid and he believes MSG is neurotoxic, as it crosses the blood- brain barrier and “over excites” neurons. I’d be interested if it does (or obviously hasn’t) changed your thoughts on this subject.
Hi John–
Yes, I’ve read Excitotoxins. And I
found Dr. Blaylock’s arguments
convincing until I dug a little
deeper. It turns out that glutamate
does indeed ‘excite’ neurons, and does
so by allowing calcium to enter the
cells. This excitation of the neuron
is offset by the ‘calming’ influence
of GABA, which acts in opposition to
glutamate. The GABA-glutamate axis in
the brain is much like the
insulin-glucagon axis in the metabolic
system. One needs both to function
properly.
Since the tiny bit of MSG used to
season foods breaks down into
glutamate and sodium – both normal
constituents of the human body, and,
in the case of glutamate, actually
made by the human body – it’s
difficult for me to image how a little
bit of glutamate added to the body’s
large circulating stores could
substantially influence the neurons.
If taken in large amounts, perhaps,
but a pinch, occasionally, I don’t
think will hurt. And maybe if a
person is deficient in magnesium there
could be a problem. Magnesium is
Nature’s calcium channel blocker, so
inadequate magnesium might not offset
the influx of calcium driven by
glutamate. This is just a hunch, but,
because – according to the latest
survey I read – about 75 percent of
Americans don’t even get the
already-too-low RDI of magnesium,
maybe it’s the widespread magnesium
deficiency that allows whatever
negative effects experienced by some
people when consuming a lot of MSG to
happen. I don’t have magnesium
consumption figures at hand for the
Japanese, but given what they eat, I
would assume they get a lot more
magnesium in the standard Japanese
diet compared to what we do in the
standard American diet.
The strongest argument for the
harmlessness of MSG is the fact that
it’s used in such large quantities in
Asia by enormous numbers of Asians
without any apparent epidemic of
negative effects. The Japanese, for
example, use MSG (and believe it’s
healthful) in large quantities and
outlive everyone else on earth despite
the fact that most of them smoke. And
they’re blowing the tops out of all
the admission processes in American
colleges, leaving US students in the
dirt, so it can’t be affecting their
cognitive abilities. If MSG were
truly harmful, I would suspect the
Japanese would suffer its ill effects.
But, again, perhaps the greater intake
of magnesium by the Japanese is
protective. Which may be why they
live longer, after all.
Cheers–
MRE
Take what you want from it, but his KGH-Style answer sure sounds way more logical and down-to-earth than all these scaremongering "OMG MSG is gonna turn you into a zombie" ones.