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Glutamate news
IGIS REFUTES ALLEGATIONS ABOUT GLUTAMATE
made in
NEW SCIENTIST - 26 OCTOBER 2002
The latest edition of New Scientist contains a
report of a paper published in a recent edition of Experimental Eye Research.
Both the paper and the report in New Scientist ignore the wealth of scientific
data which supports the safety of monosodium glutamate. The following is a
transcript of the report in the New Scientist (in italics) followed by the facts
about glutamate:
Keep an eye on the MSG
Too much monosodium glutamate could make you go
blind. Eating a lot of MSG - the flavour enhancer common in oriental and
processed foods - can damage the retina.
Researchers at Hirosaki University in Japan
have found that rats fed on diets high in MSG suffer vision loss and have
thinner retinas. Glutamate is an amino acid that acts as a neurotransmitter. It
has already been shown to cause nerve damage in experiments where it is injected
directly into the eye. But according to lead researcher Hiroshi Ohguro, his is
the first study to show that eye damage can be caused by eating food containing
MSG.
Glutamate is a safe food ingredient and a
natural component of many foods we eat as part of a normal diet such as meat,
fish, vegetables like tomatoes and mushrooms, and cheese. The body treats
glutamate in exactly the same way whether it comes from these sources or from
seasoning added to food.
In addition, the body actually produces
glutamate. It is therefore absurd to suggest that eating glutamate can have an
adverse effect.
In the study, rats were fed three different
diets for six months, containing either high or moderate amounts of MSG, or
none. In rats on the high-MSG diet, some retinal nerve layers thinned by as much
as 75 per cent. And tests that measured retinal response to light showed they
couldn't see as well. Rats on the moderate diet also had damage, to a lesser
extent (Experimental Eye Research, vol 75 p 307).
The researchers found high concentrations of
MSG in the vitreous fluid, which bathes the retina. MSG binds to receptors on
retinal cells, destroying them and causing secondary reactions that reduce the
ability of the remaining cells to relay electrical signals.
The doses of glutamate fed to the rats were
extremely high (neither of the experimental diets supplemented with glutamate
could be considered simply 'high' let alone 'moderate'). The amount of the diet
represented by added glutamate could not be replicated in a meal for human
consumption. Each day the average person consumes between 10g and 20g of
glutamate as part of their normal diet, most of which is consumed as glutamate
in the protein in foods. The amount of glutamate used as seasoning is in the
range of 0.1% to 0.8% of the food consumed (0.1 to 0.8 g/100g of food).
Ohguro acknowledges that large amounts of MSG
were used, 20 per cent of the total diet in the highest group. "Lesser
amounts should be OK," he says, "but the precise borderline amount is
still unknown."
The amount of glutamate fed to the rats
represented between 9% and 16.6% of the total diet (either 10g or 20g of
monosodium glutamate added to 100g of feed). These amounts could only be
considered abuse doses and are completely irrelevant to human nutrition or
glutamate consumption.
The amount of glutamate used to season food is
a fraction of the levels cited in this experiment (0.1% to 0.8% of food
consumed). Monosodium glutamate is a self-limiting ingredient - once an
appropriate amount has been added, using more contributes little, if any,
additional flavour. Indeed, the addition of too much monosodium glutamate, as
seasoning, can result in a decline in palatability of the food to which it is
added. At the levels indicated by the experimental diets the food is likely to
be inedible.
He says the findings might explain why, in
eastern Asia, there is a high rate of normal-tension glaucoma, a form of the eye
disease that leads to blindness without the usual increase in pressure inside
the eyeball. The higher rate, however, could also be due to genetics.
This hypothesis ignores the wealth of
scientific data which supports the safety of glutamate. Hundreds of scientific
studies have been conducted on glutamate with the focus on its use as a food
ingredient. This extensive body of research, reviewed by scientists and
regulatory authorities around the world, together with its long history of use,
demonstrates that glutamate is safe.
In 1987, the Joint Expert Committee on Food
Additives (JECFA) of the United Nations Food and Agriculture Organisation and
the World Health Organisation, having reviewed all of the scientific data on
glutamate concluded that the ingredient is safe. This review included long term,
multi-generation toxicological studies which confirmed that monosodium glutamate
does not effect retinal morphology or function.
In 1991, the European Commission's Scientific
Committee for Food (SCF) reaffirmed the safety of monosodium glutamate.
In its 1995 report to the FDA, following a
comprehensive review of the scientific literature about monosodium glutamate,
the Federation of American Societies for Experimental Biology (FASEB) concluded
that there is no difference between naturally occurring free glutamate found in
mushrooms, cheese and tomatoes and the glutamate from monosodium glutamate.
Peng Tee Khaw, a glaucoma specialist at
Moorfields Eye Hospital in London, says the amounts of MSG in the highest diet
are "a lot, lot higher than you'd eat. But if you're a sodium glutamate
junky, then you could potentially run into problems with your retina."
And while the amount of glutamate in the rats'
diets was extremely high, lower dietary intakes could produce the same effects
over several decades. This may be why people tend not to develop normal-tension
glaucoma until they are in their forties.
The allegation that "lower dietary intakes
could produce the same effects over several decades" has no basis in
science. This statement ignores what we know about glutamate's role in the body
and its metabolism. The body contains about 1,800 g of glutamate (in a 70 kg
adult) of which about 10g is free glutamate. Between 10g and 20g of glutamate is
consumed everyday and absorbed for use by the body in normal metabolism. The
body itself produces glutamate during normal metabolism - approximately 48g of
glutamate is turned over in the body everyday. In addition, the average person
excretes about 16g of glutamate everyday. Glutamate, from whatever source,
consumed as part of a normal diet would be metabolised and would not build up in
the manner described.
IGIS
24 October 2002
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