There is a ton of controversy surrounding MSG in the natural health community.
It is claimed to cause asthma, headaches, and even brain damage.
On the other hand, most mainstream sources (like the FDA) claim that MSG is safe ().
This article takes a detailed look at MSG and its health effects, examining both sides of the argument.
MSG is short for monosodium glutamate.
It is a common food additive that is used to enhance flavor. It has the e-number E621.
MSG is derived from the amino acid glutamate, or glutamic acid, which is one of the most abundant amino acids in nature.
Glutamate is one of the non-essential amino acids, meaning that the human body is able to produce it. It serves various functions in the human body, and is found in virtually all foods.
This photo shows the chemical structure of MSG:
As the name implies, monosodium glutamate (MSG) is the product of sodium (Na) and glutamate, known as a sodium salt.
The glutamate in MSG is made via fermentation of starches, but there is no chemical difference between glutamate in MSG and glutamate in natural foods.
However, glutamate in MSG may be easier for the body to access, because it isn't bound inside big protein molecules that need to be broken down.
MSG enhances the savory or meaty umami flavor of foods (). Umami is the fifth basic taste that humans sense, along with salty, sour, bitter and sweet.
It is popular in Asian cooking, and is used in all sorts of processed foods in Western countries.
The average daily intake is around 0.55-0.58 grams in the US and UK, and 1.2-1.7 grams in Japan and Korea ().
Bottom Line: Monosodium glutamate (MSG) is the sodium salt of glutamate, an amino acid found in the human body and all sorts of foods. It is a popular food additive because it enhances the flavor of foods.
Glutamate functions as a neurotransmitter in the brain.
It is an "excitatory" neurotransmitter, meaning that it excites nerve cells in order to relay its signal.
Some have claimed that MSG leads to excessive glutamate in the brain, and excessive stimulation of nerve cells.
For this reason, MSG has been referred to as an excitotoxin.
In the year 1969, injecting large doses of MSG into newborn mice was shown to cause harmful neurological effects ().
This paper ignited a fear of MSG, which remains to this day.
In 1996, a book called Excitotoxins: The Taste That Kills was published by the neurosurgeon Dr. Russell Blaylock.
In his book, he argued that nerve cells, including those in the brain, can be destroyed by the excitatory effects of glutamate from MSG.
It is actually true that increased activity of glutamate in the brain can cause harm.
It is also true that large doses of MSG can raise blood levels of glutamate. In one study, a megadose of MSG increased blood levels by 556% ().
However, dietary glutamate should have little to no effect on the human brain because it cannot cross the blood-brain barrier in large amounts ().
Overall, there doesn't seem to be any compelling evidence that MSG acts as an excitotoxin when consumed in normal amounts.
Bottom Line: Some people have claimed that the glutamate from MSG can act as an excitotoxin, leading to destruction of nerve cells. However, there are no human studies to support this.
There are some people who may experience adverse effects after consuming MSG.
This condition is called , or MSG symptom complex.
In one study, people with self-reported MSG sensitivity consumed either 5 grams of MSG, or placebo (a dummy pill).
36.1% reported reactions with MSG, compared to 24.6% with placebo ().
Symptoms included headache, muscle tightness, numbness/tingling, weakness and flushing.
What this study indicates, is that MSG sensitivity is a real thing. The threshold dose that causes symptoms may be around 3 grams in a single meal ().
However, keep in mind that 3 grams is a very large dose, about 6 times the average daily intake in the US ().
It is unclear why this happens, but some researchers speculate that such large doses of MSG enable trace amounts of glutamate to cross the blood-brain barrier and interact with neurons, leading to neuronal swelling and injury ().
MSG has also been claimed to cause asthma attacks in susceptible individuals.
One study found that 13 of 32 individuals experienced an asthma attack with large doses of MSG ().
However, other similar studies did not find any relationship between MSG intake and asthma (, , , )
Bottom Line: There is evidence that MSG can cause adverse symptoms in some individuals. The doses used in the studies were much higher than the average daily intake.
Certain foods are more satiating than others.
Eating foods that are satiating should lead to reduced calorie intake, which may help with weight loss.
There is some evidence that adding MSG to foods can have such an effect.
To investigate this, researchers had people eat MSG-flavored soups before a meal, and then measured how many calories they consumed during the meal.
These studies have shown that MSG can enhance satiety, helping people eat fewer calories at subsequent meals (, ).
It is believed that the taste of umami, provided by MSG, helps regulate appetite by stimulating receptors found on the tongue and wall of the digestive tract ().
This triggers the release of appetite-regulating hormones like cholecystokinin and GLP-1 (, ).
However, take these results with a grain of salt because other studies have shown MSG to increase, not decrease, calorie intake ().
Bottom Line: Several studies have examined the effects of MSG on calorie intake. Some studies showed a decrease, and others an increase.
Intake of MSG has been linked to weight gain from the start.
This is because injecting high doses of MSG into the brains of rats and mice causes them to become obese (, ).
However, this has little, if any, relevance to dietary intakes of MSG in humans.
That being said, there are several observational studies that link MSG consumption to weight gain and obesity.
In China, increased MSG consumption has been linked to weight gain on several occasions, with the average intake ranging between 0.33-2.2 grams per day (, ).
However, in Vietnamese adults, an average intake of 2.2 grams per day was not associated with being overweight ().
There was also a study linking increased MSG intake with weight gain and metabolic syndrome in Thailand, but this study had a number of flaws and probably should not be taken too seriously (, ).
One recent controlled trial in humans showed that MSG raised blood pressure and increased frequency of headaches and nausea ().
However, this study used unrealistically high doses.
Bottom Line: Some observational studies link MSG intake to weight gain, but the results are weak and inconsistent. One controlled trial using extremely high doses found MSG to raise blood pressure.
Depending on who you ask, MSG is either 100% safe or a dangerous neurotoxin. As is often the case in nutrition, the truth is somewhere between the two extremes.
Looking at the evidence, it seems pretty clear that MSG is safe in moderate amounts.
However, megadoses, as in 6-30 times the average daily intake (consumed in a single dose) may cause harm.
If you personally feel that you react adversely to MSG, then you should avoid it. Plain and simple.
But if you can tolerate MSG without any symptoms, then there doesn't seem to be any compelling reason to avoid it.
That being said, MSG is generally found in processed, low-quality foods, stuff that you shouldn't be eating much of anyway.
If you already eat a balanced, real food-based diet, then your MSG intake should be low by default.