Health concerns
MSG intolerance
There have been reports of allergies and/or sensitivities to MSG, sometimes attributed to the free glutamic acid component, which has been blamed for causing a wide variety of physical symptoms such as
migraines,
nausea, digestive upsets, drowsiness, heart
palpitations,
asthma,
anaphylactic shock, and a myriad of other complaints. "
Chinese restaurant syndrome" is often used as an example of the symptoms purported to be caused by MSG.
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
- weak pulse
- violent dreams
- 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.
Excitotoxicity
Glutamic acid is an amino acid commonly found in foods. Because MSG is absorbed very quickly (unlike glutamic acid-containing proteins in foods), it is known that MSG could spike blood plasma levels of glutamate.
[4] [5] [6] Glutamic acid is in a class of chemicals known as
excitotoxins. Abnormally high levels of excitotoxins have been shown in hundreds of animals studies to cause damage to areas of the brain unprotected by the blood brain barrier and that a variety of chronic diseases can arise out of this neurotoxicity.
[7] [8] The debate among scientists on the significance of these findings has been raging since the early 1970's, when Dr. John Olney found that high levels of glutamic acid caused damage to the brains of infant mice.
[9] The debate is complex and has focused on several areas:
- Whether the increase in plasma glutamate levels from typical ingestion levels of MSG is enough to cause neurotoxicity in one dose or over time.
- Whether humans are susceptible to the neurotoxicity from glutamic acid seen in some animal experiments.
- Whether neurotoxicity from excitotoxins should consider the combined effect glutamic acid and other excitotoxins such as aspartic acid from aspartame.
At a meeting of the Society for Neuroscience, the delegates had a split opinion on the issues related to neurotoxic effects from excitotoxic amino acids found in some additives such as MSG.
[10]
Some scientists believe that humans and other primates are not as susceptible to excitotoxins as rodents and therefore there is little concern with glutamic acid from MSG.
[11] [12] While they agree that the combined effects of all food-based excitotoxins should be considered
[13], their measurements of the blood plasma levels of glutamic acid after ingestion of monosodium glutamate and aspartame demonstrate that there is not a cause for concern.
[14] Other scientists feel that primates are susceptible to excitotoxic damage
[15] and that humans concentrate excitotoxins in the blood more than other animals.
[16] Based on these findings, they feel that humans are approximately 5-6 times more susceptible to the effects of excitotoxins than rodents are.
[17] While they agree that typical use of MSG does not spike glutamic acid to extremely high levels in adults, they are particularly concerned with potential effects in infants and young children
[18] and the potential long-term neurodegenerative effects of small-to-moderate spikes on plasma excitotoxin levels.
[19]
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צ'אט
17-04-2006, 16:34
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