A. Case study
B. More information
C. Editors' comments
E. CPD questions (South Africa, Australia)
A. Case study
A 41-year-old man
experienced 2 episodes of adverse effects (red rash, headache, sweating
and nausea) after eating at restaurants: once at a Chinese restaurant
and once at a bistro. He had never experienced these symptoms on any
other occasion and had no previous history of allergy. This is what
he ate on these occasions:
Chinese restaurant: tuna steak on egg noodles with 500ml red
Bistro: a small bread roll with butter, salmon sushi starter,
half chicken with a tomato-based sauce, and 3 beers.
The symptoms appeared
within 30 minutes after ingestion and spontaneously disappeared within
4 hours after the meal. He had eaten at these restaurants before without
experiencing any adverse reactions, but had, however, never eaten these
specific dishes at these restaurants. He had had similar dishes at home,
but not in the same amounts or combinations; e.g., he hadn't had sushi
followed by chicken and accompanied by beer. He confessed to having
had larger amounts of the food and alcoholic beverages on these occasions
than he would normally have at home.
What type of reaction could this be?
a. Food poisoning
b. Food allergy
c. Food or food additive intolerance
a. Shortly after the onset of symptoms of the first reaction, the patient
visited a general practitioner. The doctor excluded food poisoning as
a cause, on consideration of the quick resolution of symptoms and the
absence of diarrhea, which is usually a main feature of food poisoning.
He suspected a food allergy and asked for a total IgE test to be done.
The results were within the normal range.
b and c. The fact
that the total IgE test was normal excluded immediate IgE hypersensitivity,
but did not exclude non-IgE hypersensitivity. The type of red rash could
give a clue about the type of reaction. If it were hives/urticaria,
allergy would be a more likely cause, but erythema is usually more characteristic
of an intolerance. The GP the patient visited described the rash as
The type of symptoms
experienced, and their onset and duration, pointed to an intolerance
rather than an allergy. If it were an intolerance, this could explain
why the patient had eaten these dishes before without developing symptoms.
Intolerances usually show a dose-response. Even though the patient has
eaten these foods before, on the later occasions he could have eaten
a higher dose, which elicited the reaction. The history and results
therefore suggested that an intolerance was the more likely cause.
What, in each of the foods he ate, could have caused the reaction? The
following are constituents present in each food that could result in
an intolerance-type reaction:
Egg noodles: gluten
Red wine: alcohol, histamine, yeast
Bread roll: yeast, gluten
Butter: nothing at significant levels
Salmon sushi: histamine
Chicken: nothing at significant levels
Tomato-based sauce: histamine, MSG, serotonin, tyramine and salicylates
Beer: alcohol, bromelin, histamine, nitrates, sulphites, sulphur dioxide,
tartrazine, tyramine and yeast
Also, several of the dishes besides the tomato-based sauce could have
contained MSG, as many restaurants add large amounts to their food.
as gluten, alcohol, yeast, serotonin and tartrazine would most likely
not have been the cause of the adverse reactions, as they are present
in many other foods that the patient had eaten before without experiencing
The following should
therefore be considered as possible causes:
a. MSG intolerance (also known as Chinese Restaurant Syndrome)
b. Histamine intolerance
c. Tyramine intolerance
a. MSG: Although it is difficult to determine the exact level of MSG
of each meal, none of the foods eaten (except tomato) were significant
sources of MSG. The seasoning, however, would probably contain MSG.
Note that the association between Chinese restaurant syndrome and MSG
intake has not been proven beyond doubt. What we do know about MSG sensitivity
is the following:
i. Adverse reactions are more likely to occur when MSG-containing food
is eaten on an empty stomach. This patient had a bread roll before his
main meal at the bistro and thus did not have an empty stomach.
ii. The reported duration of symptoms is about 2 hours, but longer periods
have been recorded.
iii. Because alcohol was taken with the food, it could have increased
the severity and onset of the symptoms.
When questioned about his MSG intake, the patient said that his family
did use significant amounts of MSG-containing seasonings and processed
foods. MSG would therefore be an unlikely cause of the adverse reactions,
as he had never experienced these symptoms when eating larger quantities
of MSG at home.
b. Histamine: Most
of the foods the patient had at both restaurants are significant sources
of histamine. On both occasions he had fish, which can contain large
amounts of histamine when it has not been stored properly. (The reactions
are also known as scromboid poisoning.) Fish could therefore result
in adverse reactions on one occasion but not another (when the histamine
levels are lower). This could explain why he had never experienced a
reaction before. On both occasions, the histamine level of the meals
was high enough to elicit a reaction.
c. Tyramine: Only
some of the foods the patient had were significant sources of tyramine.
However, it cannot be ruled out as a possible cause yet.
Based on the clinical
history, the reactions were most likely due to histamine and/or tyramine
rather than to MSG. There is no easy test to diagnose sensitivity to
histamine or tyramine. For prevention of future reactions, the patient
was given a list of foods that contain high levels of these substances.
He was advised to be careful not to eat high levels of them at one meal
and to always make sure that the fish that he ate was fresh.
|TIP for Allergy
find out which constituents are present in each of the foods,
as was done with this case study, enter the specific food
into the search function, "Items, substances & allergens".
The "Possible additional constituents" can be found
on the right of the screen. This can help to determine what
constituent the person is reacting to in a specific food or
product. The risk of a person reacting to a specific constituent
is indicated next to each constituent with a number ranging
from 0 to 5 (0 indicating no risk and 5 indicating a high
B. More information:
Monosodium glutamate (MSG) is one of the glutamate salts of glutamic
acid (or L-glutamic acid), an amino acid. It consists of glutamate,
salt and water. In the food industry, MSG is used for developing and
enhancing the flavor of, predominantly, savory products.1
Glutamic acid is
naturally present in most foods in either the free form or bound to
peptides and proteins.2 In its free form, it is present in mushrooms,
tomatoes, soy sauce and other fermented soy products. It is a major
constituent of food proteins (in some foods comprising 20% of the total
amino acid content) such as meat, fish, milk and some vegetables. Regardless
of dietary source (protein, protein hydrolysates or salts of free glutamic
acid, including MSG), all glutamate molecules that are absorbed are
structurally identical and are metabolized in the same way. Once glutamate
is ingested, our bodies make no distinction among the origins.3
MSG does not have a distinct taste of its own, but adds flavor to other
foods. Its taste is different from the four basic tastes (sweet, sour,
salty, bitter), and has been named "umami" by the Japanese.1
Umami describes the savoriness, deliciousness or succulence of a food
and has been proposed as a fifth taste sensation.4 MSG is also known
to enhance the perception of sweetness and saltiness, and to diminish
that of sourness and bitterness.2 The distinctive taste of MSG has
a self-limiting characteristic: once the correct amount has been used
in a product, any additional amount added contributes little or no additional
taste to the product. Excessive consumption of MSG can result in a decrease
in taste sensitivity.
acid, which occurs in virtually all proteins, has no umami effect; only
the free form has this property.4 Besides MSG, other salts
of free glutamate have a taste-enhancing effect: examples are monopotassium
glutamate and monoammonium glutamate.5 MSG is commonly used
to enhance the natural flavors of meats, poultry, seafood, soups and
stews, but has no flavor-improving effect on some foods such as confectionery
and dairy products, soft drinks, fruit drinks, and desserts. MSG will
not improve the flavor of poor-quality food.
MSG in the food
comment by FACTS's food scientist, Maritza
Originally, MSG was produced from seaweed, but today MSG is produced
commercially through natural fermentation of molasses from sugar
cane or sugar beets, or through natural fermentation of starch
or corn sugar. It is available as white or almost white crystals
It is used
as a flavor enhancer (stimulating taste buds or increasing saliva
production) or a flavor potentiator and is often found in Chinese,
Japanese and Southeastern Asian foods. Foods that frequently contain
MSG include the following: canned meats, prepared dinners and
side dishes, canned soups, dry soup mixes, gravy and seasoning
mixes, cookies and crackers, cured meats, smoked meats and sausages,
diet foods, freeze-dried foods, frozen foods, potato chips, prepared
snacks, prepared salads, salad dressings and mayonnaise, croutons,
bottled and canned sauces, and spices and seasonings.
70% less sodium than sodium chloride (12% vs 39%). For an equal
sensation of saltiness, the sodium provided by sodium chloride
can be reduced and compensated for by much lower amounts of MSG.
By adding MSG appropriately, sodium chloride content can be reduced
by 30-40% while maintaining the same perception of saltiness.4
All the forms
of glutamic acid and its salts are commonly known as glutamate
in the food industry. MSG is generally used at a relatively low
percentage in foods: its common usage levels range from 0.1 to
0.8%. Foods with naturally occurring glutamates, such as Parmesan
cheese, can contain as much as 1g of MSG per 100g. The average
daily intake of MSG in adults is estimated to be 0.3-1g in industrialized
countries, but can be higher occasionally, depending on the MSG
content of individual food items and an individual's taste preferences.
As much as 6g of MSG may be ingested in a highly seasoned oriental
meal, and a single bowl of wonton soup may contain 2.5g of MSG.3,5,6
reactions to MSG have been reported?
There is an ongoing debate concerning whether MSG does cause any of
the alleged adverse reactions.3 There is little evidence
that MSG causes adverse effects at normal levels of consumption. The
following symptoms and conditions have been associated with the consumption
Restaurant Syndrome/MSG symptom complex/Kwok's syndrome: These
names refer to a syndrome caused by the ingestion of MSG-rich
food, typically at Chinese restaurants. Symptoms experienced usually
include one or more of the following: headache/migraine, facial
flushing, numbness and pain in the back of the neck, feeling of
pressure or pain in the face, feeling of pressure in the upper
chest muscles, pins and needles in upper limbs, blurred vision,
dizziness, problems with balance, sweating, nausea and vomiting,
diarrhoea, changes in mood, abdominal pain and cramps, weakness,
thirst, heart palpitations, chills and shaking.3,7
usually occur within 15-30 minutes of eating a meal high in MSG
and continue for about 2 hours.3,7 There is evidence
that reactions occur only after ingestion of MSG on an empty stomach,
as in a soup at the beginning of a meal.
However, many studies
have failed to show a relationship between this syndrome and MSG intake.
But some clinicians have estimated that the prevalence of "Chinese
Restaurant Syndrome" may be as high as 1.8% of the adult population.5
Although this syndrome
has been associated with eating at Chinese restaurants, it should be
noted that foods from French or even Australian restaurants might contain
more MSG than Chinese food. However, in line with the suggestion that
adverse reactions occur only if MSG is ingested on an empty stomach,
one should bear in mind that the hors d'oeuvres that are served before
an MSG-rich meal in some countries and cultures may protect the consumer
from the effects of the MSG.
The evidence is clear that MSG can be neurotoxic at high doses in several
animal species. But there is substantial disagreement about the significance
of this observation for humans. The dose of MSG ingested to induce this
effect in animals is many times higher (10- to 40 times) than those
occurring in humans under normal conditions of MSG use, and far exceeds
maximum palatable doses. To be effective as a neurotoxin in animals,
MSG must be administered in relatively high concentrations in a very
short time. In humans, MSG is ingested as a food flavoring at low concentrations
over a relatively long period, the duration of a meal.2,5,8,9
3. Asthma: Studies
have suggested that MSG induces or -exacerbates asthma (with especially
bad effects in patients with severe, poorly controlled asthma). Asthmatics
have been found to react 6-12 hours after consuming MSG in doses of
0.5-2.5g, but subsequent studies have failed to confirm these findings.3,5,6,7,8,10,11,12
4. Skin manifestations:
Although many studies have investigated the association between additives
and skin reactions, most of these studies have been poorly designed.
There have been some reports that MSG induces or exacerbates urticaria,
angioedema and atopic dermatitis.5,13,14,15
5. There has been
a report of 4 women diagnosed with fibromyalgia syndrome, which they
had manifested for 2 to 17 years. After undergoing multiple treatment
modalities with limited success, MSG or MSG plus aspartame was excluded
from their diets. All had complete, or nearly complete, resolution of
their symptoms within months and had recurrence of symptoms whenever
MSG was ingested.16
has been associated with MSG ingestion, but there has also been a great
deal of criticism of these studies.5,17,18,19
7. Taken orally,
MSG has been found to stimulate gastric secretion. It is therefore sometimes
recommended as an adjuvant in combined therapy of atrophic gastritis.20
8. Depression, irritability,
and other mood changes have also been reported.7
The mechanism of
action has not been established, but reactions appear to be due to intolerance.
The effects of MSG may therefore be dose-related, and responses may
vary between individuals.
How safe is MSG?
MSG has been safely used as a food ingredient for more than 60 years.5
It is one of the most thoroughly researched food ingredients, as has
been confirmed by regulatory and scientific agencies around the world.
MSG is safe for the majority of the population, although it may be responsible
for adverse reactions in a small number of individuals. Nevertheless,
an ongoing debate exists concerning whether MSG causes any of the alleged
In 1958 the United
States Food and Drug Administration (FDA) classified L-glutamic acid
and hydrolyzed protein products containing L-glutamic acid (including
monosodium glutamate and hydrolyzed vegetable proteins) as generally
recognized as safe (GRAS). This status was reaffirmed when the FDA Hypersensitivity
Committee in 1986 and the FDA Health Hazards Evaluation Board in 1990
concluded that dietary intake of glutamates does not present a hazard
to human health and requires no additional regulatory action. Glutamates
were declared safe at current consumption levels for the general population,
including children and pregnant and lactating women.3 Glutamate
was found not to readily pass through the placental barrier, so that
it would not affect the fetus. The ingestion of MSG has also not been
associated with elevated levels of the substance in breast milk. Infants
were found to metabolize MSG similarly to adults and therefore not to
be at a higher risk of adverse effects.2,9
FAO/WHO Expert Committee on Food Additives (JECFA) allocated an
"acceptable daily intake (ADI) not specified" to glutamic
acid and its salts in1988, which indicates that there were no
toxicological concerns associated with their use as food additives
in accordance with good manufacturing practice (GMP). The Scientific
Committee for Food (SCF) of the European Commission made a similar
evaluation in 1991, placing MSG in the safest category for food
MSG is permitted
worldwide, although in some countries and for some types of foods,
maximum concentration limits apply. Other salts of glutamic acids
that are occasionally used are potassium, calcium and ammonium
glutamic acids. These salts are not permitted worldwide. Most
countries' legislation requires that the presence of MSG be indicated
on the label of any product.
Drinking alcoholic beverages while eating MSG-containing foods would
probably increase the severity and rate of onset of symptoms, as alcohol
seems to increase the rate of absorption of many foods, including MSG.
It should be kept in mind that alcoholic beverages contain many constituents
that, by themselves, could elicit adverse reactions in sensitised individuals.
For a confirmed MSG sensitivity, the following should be kept in mind:
Eating MSG-containing food on an empty stomach seems to exacerbate
or even precipitate adverse effects.
Glutamate is also present in monopotassium glutamate, monoammonium
glutamate, calcium glutamate and other salts of glutamic acid. Some
MSG-sensitive persons may react to these salts also.
Some practitioners have noticed a deficiency of Vitamin B6 (pyridoxine)
in a number of MSG-sensitive persons. This factor could retard hepatic
catabolism of glutamate, thus prolonging high plasma glutamate levels
and exacerbating symptoms.7
||compiled by Karen du Plessis
Food & Allergy Consulting & Testing Services (FACTS)
PO Box 565
Comments by our editors
Individuals who claim to experience adverse effects to MSG
must be frustrated when they are not believed. It is important
for the health professional to listen carefully to their complaints,
and also whether their symptoms are attributable to some other
allergic condition, intolerance or other constituent of the food
For more information
on this subject and other allergy and intolerance related topics, visit:
To join a professional
food allergy discussion list where this subject can be discussed further,
go to http://groups.yahoo.com/group/AllergyDietitian
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1. Fernstrom JD. Second International Conference on Glutamate: Conference
Summary. Journal of Nutrition. 2000;130:1077S-1079S.
2. Garattini S. Glutamic Acid, Twenty Years Later. Journal of Nutrition.
3. Geha RS, Beiser A, Ren C, Patterson R, Greenberger PA, Grammer LC,
Ditto AM, Harris KE, Shaughnessy MA, Yarnold PR, Corren J, Saxon A.
Review of alleged reaction to monosodium glutamate and outcome of a
multicenter double-blind placebo-controlled study. J Nutr. 2000 Apr;130(4S
4. Löliger J. Function and Importance of Glutamate for Savory Foods.
Journal of Nutrition. 2000;130:915S-920S.
5. Metcalfe DD, Sampson HA, Simon RA. Food allergy: adverse reactions
to foods and food additives 3rd Edition. Blackwell Publishing, 2003.
6. Allen DH, Delohery J, Baker G. Monosodium L-glutamate-induced asthma.
J Allergy Clin Immunol 1987;80(4):530-7.
7. Joneja JV. Dietary management of food allergies and intolerances
- a comprehensive guide 2nd edition. J.A. Hall Publications Ltd., USA,
8. Walker R. The significance of excursions above the ADI. Case study:
monosodium glutamate. Regul Toxicol Pharmacol. 1999 Oct;30(2 Pt 2):S119-21.
9. Walker R, Lupien JR. The safety evaluation of monosodium glutamate.
J Nutr. 2000 Apr;130(4S Suppl):1049S-52S.
10. Woessner KM, Simon RA, Stevenson DD. Monosodium glutamate sensitivity
in asthma. J Allergy Clin Immunol. 1999 Aug;104(2 Pt 1):305-10.
11. Woods RK, Weiner JM, Thien F, Abramson M, Walters EH. The effects
of monosodium glutamate in adults with asthma who perceive themselves
to be monosodium glutamate-intolerant. J Allergy Clin Immunol 1998;101(6
12. Stevenson DD. Monosodium glutamate and asthma. J Nutr. 2000 Apr;130(4S
13. Simon RA. Additive-induced urticaria: experience with monosodium
glutamate (MSG). J Nutr. 2000 Apr;130(4S Suppl):1063S-6S.
14. Squire EN, Jr. Angio-oedema and monosodium glutamate. Lancet 1987;329:988.
15. Van Bever HP, Docx M, Stevens WJ. Food and food additives in severe
atopic dermatitis. Allergy 1989;44(8):588-594.
16. Smith JD, Terpening CM, Schmidt SO, Gums JG. Relief of fibromyalgia
symptoms following discontinuation of dietary excitotoxins. Ann Pharmacother
17. Scopp AL. MSG and hydrolyzed vegetable protein induced headache:
review and case studies. Headache. 1991 Feb;31(2):107-10.
18. Sands GH, Newman L, Lipton R. Cough, exertional, and other miscellaneous
headaches. Med Clin North Am 1991;75(3):733-747.
19. Leira R, Rodriguez R. Diet and migraine. Revista de Neurologia 1996;24(129):534-8.
20. Kochetkov AM, Shlygin GK, Loranskaia TI, Vasilevskaia LS, Kondrashev
SI. The use of monosodium glutamate in the combined therapy of patients
with atrophic gastritis. Vopr Pitan 1992;(5-6):19-22.
Questions (For South African dietitians only. Australian
dietitians: where you have relevant learning goals, CPD hours related
to this resource can be included in your APD log.)
You can obtain 2 CPD points for reading
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CPD reference number: DT03/3/109/13
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2. Read the newsletter and answer the questions.
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ALL THE QUESTIONS
(There is only
one correct answer per question.)
1. Which of the following statements is false?
(a.) MSG is one of the glutamate salts of glutamic acid.
(b.) Glutamic acid is an amino acid.
(c.) Glutamic acid is naturally present in many foods.
(d.) Free glutamate is better absorbed than the bound form.
2. Which of the
following statements regarding the umami taste sensation is false?
(a.) It is claimed to be the fifth taste sensation.
(b.) It describes the savoriness, deliciousness or succulence of a food.
(c.) The more MSG is added, the better the taste.
(d.) The protein-bound glutamic acid has no umami effect.
3. Which of the
following foods' flavor will be enhanced the most (if at all) by MSG?
(c.) Soft drinks
4. By what percentage
can the addition of sodium chloride be reduced, while maintaining the
same perception of saltiness, by adding the appropriate amount of MSG
to a product?
5. Which of the
following is not true concerning what we know about "Chinese Restaurant
(a.) Symptoms that are typically experienced include headache, numbness
and pain in the back of the neck, sensation of facial pressure, sweating,
nausea and vomiting.
(b.) The onset of symptoms is usually delayed by 6-8 hours.
(c.) Symptoms appear to occur only after ingestion of MSG on an empty
(d.) The estimated prevalence is as high as 1.8% of the adult population.
6. Studies have
indicated (although not yet conclusively proven) that MSG can cause
which of the following symptoms?
(d.) All of the above
7. True or false:
MSG has been found to be neurotoxic in humans when ingested in relatively
high concentrations in a very short time.
8. True or false:
MSG is safe at current consumption levels for the general population,
including children and pregnant and lactating women.
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