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 official sources like the FDA claim that MSG is safe (1).

This article examines MSG and its health effects, exploring both sides of the argument.

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MSG is short for monosodium glutamate.

It is a common food additive — with the e-number E621 — that is used to enhance flavor.

MSG is derived from the amino acid glutamate, or glutamic acid, which is one of the most abundant amino acids in nature.

Glutamic acid is a non-essential amino acid, meaning that your body can produce it. It serves various functions in your body and is found in nearly all foods.

Chemically, MSG is a white crystalline powder that resembles table salt or sugar. It combines sodium and glutamic acid, known as a sodium salt.

The glutamic acid in MSG is made by fermenting starches, but there is no chemical difference between the glutamic acid in MSG and that in natural foods.

However, the glutamic acid in MSG may be easier to absorb because it isn't bound inside big protein molecules that your body needs to break down.

MSG enhances the savory, meaty umami flavor of foods. Umami is the fifth basic taste, along with salty, sour, bitter and sweet (2).

This additive is popular in Asian cooking and used in various processed foods in the West.

The average daily intake of MSG is 0.55–0.58 grams in the US and UK and 1.2–1.7 grams in Japan and Korea (3).

Summary MSG is the sodium salt of glutamic acid, an amino acid found in your body and most foods. It is a popular food additive because it enhances flavor.

Glutamic acid functions as a neurotransmitter in your brain.

It is an excitatory neurotransmitter, meaning that it stimulates nerve cells in order to relay its signal.

Some people claim that MSG leads to excessive glutamate in the brain and excessive stimulation of nerve cells.

For this reason, MSG has been labeled an excitotoxin.

Fear of MSG dates as far back as 1969, when a study found that injecting large doses of MSG into newborn mice caused harmful neurological effects (4).

Since then, books like Russell Blaylock's "Excitotoxins: The Taste That Kills" have kept this fear of MSG alive.

It’s true that increased glutamate activity in your brain can cause harm — and that large doses of MSG can raise blood levels of glutamate. In one study, a megadose of MSG increased blood levels by 556% (5).

However, dietary glutamate should have little to no effect on your brain, as it cannot cross the blood-brain barrier in large amounts (6).

Overall, there is no compelling evidence that MSG acts as an excitotoxin when consumed in normal amounts.

Summary While some people assert that the glutamate from MSG can act as an excitotoxin, leading to the destruction of nerve cells, no human studies support this.

Some people may experience adverse effects from consuming MSG.

This condition is called Chinese restaurant syndrome or MSG symptom complex.

In one study, people with self-reported MSG sensitivity consumed either 5 grams of MSG or a placebo — 36.1% reported reactions with MSG compared to 24.6% with a placebo (7).

Symptoms included headache, muscle tightness, numbness, tingling, weakness and flushing.

The threshold dose that causes symptoms seems to be around 3 grams per meal. However, keep in mind that 3 grams is a very high dose — about six times the average daily intake in the US (1, 3).

It is unclear why this happens, but some researchers speculate that such large doses of MSG enable trace amounts of glutamic acid to cross the blood-brain barrier and interact with neurons, leading to brain swelling and injury (8).

Some claim that MSG also causes asthma attacks in susceptible individuals.

In one 32-person study, 40% of participants experienced an asthma attack with large doses of MSG (9).

However, other similar studies did not find any relationship between MSG intake and asthma (10, 11, 12, 13)

Summary While MSG can cause adverse symptoms in some people, doses used in studies were much higher than the average daily intake.

Certain foods are more filling than others.

Eating filling foods should reduce your calorie intake, which may aid weight loss.

Some evidence suggests that MSG may help you feel full.

Studies note that people who consume soups flavored with MSG eat fewer calories at subsequent meals (14, 15).

MSG’s umami flavor may stimulate receptors found on your tongue and in your digestive tract, triggering the release of appetite-regulating hormones (16, 17, 18).

That said, other studies indicate that MSG increases — rather than decreases — calorie intake (19).

Therefore, it’s best not to rely on MSG to help you feel full.

Summary While some studies suggest that MSG may reduce your calorie intake, others claim that it boosts intake.

Some people associate MSG with weight gain.

In animal studies, injecting high doses of MSG into the brains of rats and mice caused them to become obese (20, 21).

However, this has little — if any — relevance to dietary intake of MSG in humans.

That said, several human studies link MSG consumption to weight gain and obesity.

In China, increased MSG intake has been linked to weight gain — with average intake ranging from 0.33–2.2 grams per day (3, 22).

However, in Vietnamese adults, an average intake of 2.2 grams per day was not associated with being overweight (23).

Another study tied increased MSG intake to weight gain and metabolic syndrome in Thailand — but it has been criticized for methodological flaws (24, 25).

In a controlled trial in humans, MSG raised blood pressure and increased the frequency of headaches and nausea. However, this study used unrealistically high doses (26).

More human studies are needed before full claims can be made about MSG’s link to obesity or metabolic disorders.

Summary Though some studies link MSG intake to weight gain, the results are weak and inconsistent. More studies are necessary.

Depending on who you ask, MSG is either perfectly safe or a dangerous neurotoxin.

The truth lies somewhere in between.

Evidence indicates that MSG is safe in moderate amounts. However, megadoses may cause harm.

If you react adversely to MSG, you shouldn’t eat it. That said, if you don’t experience side effects, there’s no compelling reason to avoid it.

Keep in mind that MSG is generally found in processed, low-quality foods — which you should avoid or limit anyway.

If you already eat a balanced diet with plenty of whole foods, you shouldn’t have to worry about high MSG intake.