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Monosodium Glutamate
August 31, 1995
Monosodium glutamate (MSG) is used as a flavor enhancer in
a variety of foods prepared at home, in restaurants, and by
food processors. Its use has become controversial in the past
30 years because of reports of adverse reactions in people
who've eaten foods that contain MSG. Research on the role
of glutamate--a group of chemicals that includes MSG--in the
nervous system also has raised questions about the chemical's
safety.
Studies have shown that the body uses glutamate, an amino
acid, as a nerve impulse transmitter in the brain and that
there are glutamate-responsive tissues in other parts of the
body, as well. Abnormal function of glutamate receptors has
been linked with certain neurological diseases, such as Alzheimer's
disease and Huntington's chorea. Injections of glutamate in
laboratory animals have resulted in damage to nerve cells
in the brain. Consumption of glutamate in food, however, does
not cause this effect. While people normally consume dietary
glutamate in large amounts and the body can make and metabolize
glutamate efficiently, the results of animal studies conducted
in the 1980s raised a significant question: Can MSG and possibly
some other glutamates harm the nervous system? A 1995 report
from the Federation of American Societies for Experimental
Biology (FASEB), an independent body of scientists, helps
put these safety concerns into perspective and reaffirms the
Food and Drug Administration's belief that MSG and related
substances are safe food ingredients for most people when
eaten at customary levels.
The FASEB report identifies two groups of people who may develop
a condition the report refers to as "MSG symptom complex."
One group is those who may be intolerant to MSG when eaten
in a large quantity. The second is a group of people with
severe, poorly controlled asthma. These people, in addition
to being prone to MSG symptom complex, may suffer temporary
worsening of asthmatic symptoms after consuming MSG. The MSG
dosage that produced reactions in these people ranged from
0.5 grams to 2.5 grams.
Although FDA has not fully analyzed the FASEB report, the
agency believes that the report provides the basis to require
glutamate labeling. FDA will propose that foods containing
significant amounts of free glutamate (not bound in protein
along with other amino acids) declare glutamate on the label.
This would allow consumers to distinguish between foods with
insignificant free glutamate levels and those that might contribute
to a reaction.
What Is MSG?
MSG is the sodium salt of the amino acid glutamic acid and
a form of glutamate. It is sold as a fine white crystal substance,
similar in appearance to salt or sugar. It does not have a
distinct taste of its own, and how it adds flavor to other
foods is not fully understood. Many scientists believe that
MSG stimulates glutamate receptors in the tongue to augment
meat-like flavors.
Asians originally used a seaweed broth to obtain the flavor-
enhancing effects of MSG, but today MSG is made by a fermenting
process using starch, sugar beets, sugar cane, or molasses.
Glutamate itself is in many living things: It is found naturally
in our bodies and in protein-containing foods, such as cheese,
milk, meat, peas, and mushrooms.
Some glutamate is in foods in a "free" form. It
is only in this free form that glutamate can enhance a food's
flavor. Part of the flavor-enhancing effect of tomatoes, certain
cheeses, and fermented or hydrolyzed protein products (such
as soy sauce) is due to the presence of free glutamate.
Hydrolyzed proteins, or protein hydrolysates, are acid- treated
or enzymatically treated proteins from certain foods. They
contain salts of free amino acids, such as glutamate, at levels
of 5 to 20 percent. Hydrolyzed proteins are used in the same
manner as MSG in many foods, such as canned vegetables, soups,
and processed meats.
Scientific
Review
In 1959, FDA classified MSG as a "generally recognized
as safe," or GRAS, substance, along with many other common
food ingredients, such as salt, vinegar, and baking powder.
This action stemmed from the 1958 Food Additives Amendment
to the Federal Food, Drug, and Cosmetic Act, which required
premarket approval for new food additives and led FDA to promulgate
regulations listing substances, such as MSG, which have a
history of safe use or are otherwise GRAS.
Since 1970, FDA has sponsored extensive reviews on the safety
of MSG, other glutamates and hydrolyzed proteins, as part
of an ongoing review of safety data on GRAS substances used
in processed foods.
One such review was by the FASEB Select Committee on GRAS
Substances. In 1980, the committee concluded that MSG was
safe at current levels of use but recommended additional evaluation
to determine MSG's safety at significantly higher levels of
consumption. Additional reports attempted to look at this.
In 1986, FDA's Advisory Committee on Hypersensitivity to Food
Constituents concluded that MSG poses no threat to the general
public but that reactions of brief duration might occur in
some people.
Other reports gave similar findings. A 1991 report by the
European Communities' (EC) Scientific Committee for Foods
reaffirmed MSG's safety and classified its "acceptable
daily intake" as "not specified," the most
favorable designation for a food ingredient. In addition,
the EC Committee said, "Infants, including prematures,
have been shown to metabolize glutamate as efficiently as
adults and therefore do not display any special susceptibility
to elevated oral intakes of glutamate."
A 1992 report from the Council on Scientific Affairs of the
American Medical Association stated that glutamate in any
form has not been shown to be a "significant health hazard."
Also, the 1987 Joint Expert Committee on Food Additives of
the United Nations Food and Agriculture Organization and the
World Health Organization have placed MSG in the safest category
of food ingredients.
Scientific knowledge about how the body metabolizes glutamate
developed rapidly during the 1980s. Studies showed that glutamate
in the body plays an important role in normal functioning
of the nervous system. Questions then arose on the role glutamate
in food plays in these functions and whether or not glutamate
in food contributes to certain neurological diseases.
Anecdotal Evidence
Many of these safety assessments were prompted by unconfirmed
reports of MSG-related adverse reactions. Between 1980 and
1994, the Adverse Reaction Monitoring System in FDA's Center
for Food Safety and Applied Nutrition received 622 reports
of complaints about MSG. Headache was the most frequently
reported symptom. No severe reactions were documented, but
some reports indicated that people with asthma got worse after
they consumed MSG. In some of those cases, the asthma didn't
get worse until many hours later.
Also, several books and a TV news show have reported widespread
and sometimes life-threatening adverse reactions to MSG, claiming
that even small amounts of manufactured glutamates may cause
adverse reactions.
A problem with these unconfirmed reports is that it is difficult
to link the reactions specifically to MSG. Most are cases
in which people have had reactions after, but not necessarily
because of, eating certain foods containing MSG.
While such reports are helpful in raising issues of concern,
they do not provide the kind of information necessary to describe
who is most likely to be affected, under what conditions they'll
be affected, and with what amounts of MSG. They are not controlled
studies done in a scientifically credible manner.
1995 FASEB Report
Prompted by continuing public interest and a flurry of glutamate-related
studies in the late 1980s, FDA contracted with FASEB in 1992
to review the available scientific data. The agency asked
FASEB to address 18 questions dealing with:
- the possible role of MSG in eliciting MSG symptom complex
- the possible role of dietary glutamates in forming brain
lesions and damaging nerve cells in humans
- underlying conditions that may predispose a person to
adverse effects from MSG
- the amount consumed and other factors that may affect
a person's response to MSG
- the quality of scientific data and previous safety reviews.
FASEB held a two-day meeting and convened an expert panel
that thoroughly reviewed all the available scientific literature
on this issue.
FASEB completed the final report, over 350 pages long, and
delivered it to FDA on July 31, 1995. While not a new study,
the report offers a new safety assessment based on the most
comprehensive existing evaluation to date of glutamate safety.
Among the report's key findings:
- An unknown percentage of the population may react to
MSG and develop MSG symptom complex, a condition characterized
by one or more of the following symptoms:
- burning sensation in the back of the neck, forearms
and chest
- numbness in the back of the neck, radiating to the arms
and back
- tingling, warmth and weakness in the face, temples,
upper back, neck and arms
- facial pressure or tightness
- chest pain
- headache
- nausea
- rapid heartbeat
- bronchospasm (difficulty breathing) in MSG-intolerant
people with asthma
- drowsiness
- weakness.
- In otherwise healthy MSG-intolerant people, the MSG
symptom complex tends to occur within one hour after eating
3 grams or more of MSG on an empty stomach or without
other food. A typical serving of glutamate-treated food
contains less than 0.5 grams of MSG. A reaction is most
likely if the MSG is eaten in a large quantity or in a
liquid, such as a clear soup.
- Severe, poorly controlled asthma may be a predisposing
medical condition for MSG symptom complex.
- No evidence exists to suggest that dietary MSG or glutamate
contributes to Alzheimer's disease, Huntington's chorea,
amyotrophic lateral sclerosis, AIDS dementia complex,
or any other long-term or chronic diseases.
- No evidence exists to suggest that dietary MSG causes
brain lesions or damages nerve cells in humans.
- The level of vitamin B6 in a person's body plays a role
in glutamate metabolism, and the possible impact of marginal
B6 intake should be considered in future research.
- There is no scientific evidence that the levels of glutamate
in hydrolyzed proteins causes adverse effects or that
other manufactured glutamate has effects different from
glutamate normally found in foods.
Ingredient Listing
Under current FDA regulations, when MSG is added to a food,
it must be identified as "monosodium glutamate"
in the label's ingredient list. Each ingredient used to make
a food must be declared by its name in this list.
While technically MSG is only one of several forms of free
glutamate used in foods, consumers frequently use the term
MSG to mean all free glutamate. For this reason, FDA considers
foods whose labels say "No MSG" or "No Added
MSG" to be misleading if the food contains ingredients
that are sources of free glutamates, such as hydrolyzed protein.
In 1993, FDA proposed adding the phrase "(contains glutamate)"
to the common or usual names of certain protein hydrolysates
that contain substantial amounts of glutamate. For example,
if the proposal were adopted, hydrolyzed soy protein would
have to be declared on food labels as "hydrolyzed soy
protein (contains glutamate)." However, if FDA issues
a new proposal, it would probably supersede this 1993 one.
In 1994, FDA received a citizen's petition requesting changes
in labeling requirements for foods that contain MSG or related
substances. The petition asks for mandatory listing of MSG
as an ingredient on labels of manufactured and processed foods
that contain manufactured free glutamic acid. It further asks
that the amount of free glutamic acid or MSG in such products
be stated on the label, along with a warning that MSG may
be harmful to certain groups of people. FDA has not yet taken
action on the petition. |
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