Monosodium glutamate (MSG) is a common food additive that enhances the flavor of food. MSG sensitivity is a reaction some people may experience from the additive, although the range and seriousness of symptoms are controversial.

MSG is considered safe by the U.S. Food and Drug Administration (FDA), but a number of people and non-governmental groups contend that MSG can cause serious reactions in some people. The additive is similar to an amino acid called glutamate, which naturally occurs in many foods, as well as in the body.

As an additive, MSG excites the nerves in the tongue and brain, which boost food flavors. In the past 30 years, there have been concerns that MSG, used as a food additive, may be potentially harmful. People reported a wide range of symptoms that they associated with MSG, including headache, sweating, flushing and facial tingling.

Reactions became known informally as Chinese restaurant syndrome, because MSG is often used in Asian cooking (as well as in canned vegetables, soups and processed meats). Some critics believe MSG contributes to Alzheimer’s disease or other long-term or chronic diseases affecting the nervous system or brain. However, studies have concluded that MSG is not connected to serious or long-term reactions, and that the additive does not contribute to Alzheimer’s disease or other chronic diseases.

Several studies have found that a reaction (called MSG Symptom Complex) may occur in some people who eat large amounts of MSG, especially on an empty stomach. Studies have also suggested that people with allergies or asthma may also experience reactions, including difficulty breathing. However, these reactions have not been scientifically confirmed.

Many processed foods and restaurant dishes contain a food additive called monosodium glutamate or MSG. MSG boosts the taste of food by stimulating nerves on the tongue and in the brain.

MSG is a type of glutamate, which is an amino acid the body uses to help transmit messages within the brain. In addition to the body, glutamate is found in all foods that contain protein.

As an additive used on food, MSG appears white and crystalline, like salt, and is often used in Asian cooking. It is also commonly used in canned vegetables, clear soups and processed meats. MSG is made from fermenting starch and corn sugar (or molasses, sugar cane and sugar beets), and is considered a safe additive by the U.S. Food and Drug Administration (FDA).

However, some people are sensitive to MSG and numerous reports of wide–ranging symptoms (some corroborated and some uncorroborated) have been filed with the FDA. Some critics of MSG believe the additive (or similar additives) causes or contributes to long–term or chronic conditions, such as Alzheimer’s disease.

In response, the FDA partnered with the Federation of American Societies for Experimental Biology (FASEB) in 1992 to investigate the health effects of MSG. The FASEB reaffirmed the safety of MSG when it is consumed at normal levels by the general population.

No evidence was found that connected MSG and serious long–term reactions. Further, the report states that no evidence exists to suggest that MSG contributes to Alzheimer’s disease, Huntington’s disease or any other chronic diseases.   

According to the FDA, people who chronically suffer from adverse reactions when consuming MSG are said to be "sensitive to MSG" or "MSG intolerant." Officially suffering from an adverse MSG reaction is called MSG symptom complex and unofficially it is sometimes referred to as Chinese restaurant syndrome.

Some studies have found that people who suffer from allergies or severe and poorly controlled asthma may be prone to MSG sensitivity. There have also been reports of people with asthma having more severe asthma attacks after consuming MSG. Consuming large amounts of MSG (3 grams or more) on an empty stomach or in a clear soup are also associated with reported intolerance to the additive.

Some people react immediately after eating MSG while others may experience symptoms up to 48 hours later. Reactions to MSG vary from individual to individual and there is no evidence to suggest exactly why certain people are affected by it. For example, it is not known whether adverse reactions to MSG exacerbate underlying health conditions, or if undesirable cumulative effects are created after ingesting it over a period of years.

MSG intolerance is not an allergy because reactions do not involve the body’s immune system. After consuming food with MSG some people experience mild and temporary symptoms such as a headache, and long–term symptoms ranging from depression to insomnia. There may be one or more symptoms experienced at the same time.

Ultimately, the best way to treat MSG sensitivity is to avoid MSG. Processed foods that may contain other questionable additives should be avoided as well.

Exactly why MSG can cause symptoms in some people is not understood. MSG is a glutamate, a type of amino acid found naturally in many foods. Glutamate is also a neurotransmitter in the brain, involved in cognitive functions such as learning and memory.

At the core of the debate is whether the body treats MSG the same as it does natural or free glutamate. Scientists believe MSG is digested the same as free glutamate and therefore poses no health risk. However, some critics of MSG have argued that the difference between natural glutamate and the additive MSG (which has been processed) can be harmful. However, scientific evidence has not established that the body treats MSG any differently from natural glutamate.

Some people do have a sensitivity to MSG, which may arise after eating MSG over a period of time. The sensitivity is not considered an allergy, because it does not involve a reaction by the immune system.

Individuals who have other allergies or asthma may be more susceptible to an adverse MSG reaction. However, scientific studies designed to research the potential connection have not provided evidentiary links.

While symptoms may appear similar, monosodium glutamate (MSG) sensitivity is not a true food allergy because there is no response by the immune system to MSG.

There are both short and long term health effects, however, reportedly experienced by MSG sensitive individuals. Since physicians, researchers and governmental agencies disagree as to how to diagnosis and treat MSG sensitivity, symptoms may be difficult to define specifically or authenticate. 

According to the National Library of Medicine (NLM) and the U.S. Food and Drug Administration (FDA), some common signs and symptoms of MSG sensitivity include:

• Headache
• Chest pain
• Sweating
• Flushing
• Burning or numbness inside or around the mouth
• Burning or numbness in the back of the neck 
• Facial pressure or tightness
• Tingling, warmth and weakness in the face, temples, upper back, neck and arms
• Shortness of breath
• Weakness
• Rapid heartbeat
• Nausea
• Drowsiness

These signs and symptoms are temporary and typically appear shortly after large amounts of MSG-containing foods have been consumed.  

Asthmatics, according to the Federation of American Societies for Experimental Biology (FASEB) study, may experience the above symptoms as well as breathing difficulty. Additional studies in asthmatics have not produced consistent results to confirm these reported symptoms.

There have been a wide variety of other symptoms attributed to MSG. None of these symptoms have been corroborated by research studies. Uncorroborated symptoms include:

• Migraine
• Heart palpations
• Fatigue
• Hives
• Rash
• Diarrhea
• Bloating
• Joint pain
• Depression
• Insomnia
• Seizures
• Angina
• Hyperactivity
• Neurological disorders

There are no established ways to diagnose or treat monosodium glutamate (MSG) sensitivity. If MSG is suspected to be the cause of any symptoms, it is best to avoid MSG in packaged foods and restaurant foods and seek a physician’s care.

Patients should inquire about the ingredients in restaurant foods and avoid ordering and eating foods that contain MSG. Individuals trying to avoid MSG should also read food labels carefully and avoid purchasing or consuming products with MSG listed as an ingredient.

While the U.S. Food and Drug Administration (FDA) requires manufacturers to list MSG on the label of any food to which it is added, there are other glutamate additives that some claim may induce similar symptoms. These additives do not have to be listed on the label as containing MSG because they are chemically distinct. Despite not being scientifically proven, some people report that these additives may cause adverse reactions in people who are sensitive to MSG.

Food additives that contain glutamates include:

• Hydrolyzed protein
• Autolyzed yeast
• Sodium caseinate
• Calcium caseinate
• Textured protein
• Monopotassium glutamate
• Maltodextrin
• Modified food starch

MSG is not only used in processed foods but may also be found in dietary supplements, cosmetics, drugs and personal care products. Individuals should consult a physician for advice regarding MSG sensitivity and avoidance strategies.

There have been studies conducted to determine the safety of MSG for pregnant or lactating women which conclude that MSG does not affect women, fetuses or pass through breast milk.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions regarding monosodium glutamate (MSG) sensitivity:

1. Am I at risk for MSG sensitivity because I have asthma and/or allergies?
   
   
2. What symptoms would suggest that I suffer from MSG sensitivity?
   
   
3. Does having MSG sensitivity mean that I am allergic to MSG?
   
   
4. Does MSG sensitivity pose a danger to my overall health?
   
   
5. What types of food commonly contain MSG? Should I completely avoid foods with MSG or can I eat them in moderation?
   
   
6. Are there any other additives I should avoid?
   
   
7. Should I be concerned if I accidentally ingest a large amount of food containing MSG?
   
   
8. Are my children likely to be sensitive to MSG as well?