MSG: What Are Its Potential Side Effects?

Pictured Recipe: Spicy Broccoli & Bell Pepper Stir-Fry with Peanuts

Monosodium glutamate (MSG) is a flavor enhancer used in savory foods, including many Asian dishes and packaged foods. It's made by fermenting starch, such as sugar beets, sugar cane or molasses, which is similar to the process used to make wine, vinegar and yogurt, per the Food and Drug Administration (FDA).

MSG is said to be the source of our fifth taste quality—umami—which translates to "pleasant savory taste."

While MSG contains sodium, it's only a third of the amount that you'd get from the same amount of salt. In fact, in a 2019 study published in the journal Nutrients, researchers found that replacing table salt with MSG may reduce sodium intake. That's in addition to the FDA's declaration that MSG is generally recognized as safe (GRAS).

In addition to sodium, MSG also contains glutamic acid (aka glutamate). Glutamate is an amino acid that occurs naturally in foods like tomatoes, mushrooms and parmesan cheese.

Glutamate also acts as a neurotransmitter in our bodies. A neurotransmitter is a chemical messenger that carries messages from one nerve cell to the next.

Because of glutamate's role as a neurotransmitter, there has been some question as to whether eating too much MSG could disrupt glutamate's function as a neurotransmitter in the brain. Studies, such as the 2018 review article in the Annals of Nutrition and Metabolism, seem to have put this worry to rest, stating that there is no evidence of MSG ingestion causing disruptions in brain function.

MSG isn't always added to foods. It's also found naturally in some foods like hydrolyzed vegetable protein (HVP), autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts and protein isolate.

According to the FDA, our bodies break down the glutamate found in MSG the same way they do the glutamate found naturally in foods. The average adult in the U.S. eats about 13 grams of naturally-occurring glutamate a day, and about half a gram of MSG. However, because MSG is added to some packaged and processed foods, if your diet is high in these foods, your consumption of MSG might be higher than if you were to cook from scratch.

According to a 2019 review in Comprehensive Reviews in Food Science and Food Safety, some people have reported sensitivity and reactions after eating foods containing MSG that include headaches, difficulty breathing, weakness, flushing, dizziness, muscle tightness, numbness and fainting.

First brought to the attention of medical professionals in the 1960's, these symptoms are called MSG symptom complex. It is estimated that about 1% of the population has MSG symptom complex, per the 2019 review.

In addition to this cluster of symptoms, people have also reported worsening asthma, mild mood changes, heart palpitations and chest pain after eating MSG.

While it's difficult to argue with anyone's symptoms, this same review suggests that the studies that support these symptoms being specifically related to the ingestion of MSG were very small and not well-designed. Some of the studies also injected study participants with amounts of MSG that anyone is unlikely to consume from eating food containing MSG. So while the symptoms may be related to MSG, researchers have yet to prove the connection.

There may be one caveat though. According to the same 2019 review, several studies have shown that eating large doses of MSG may lead to classic symptoms of MSG symptom complex when the MSG is consumed without any food and on an empty stomach. The chances of you eating a spoonful of straight MSG seems to be highly unlikely though, so these studies do not translate to real life.

Researchers are often studying the effects of taste, smell and texture on food consumption. A 2022 review in Frontiers in Nutrition suggests that eating foods with higher umami qualities has been shown to reduce subsequent energy intake. For example, if you start your meal with a soup containing MSG, you might eat less of the actual meal.

These same researchers also state that there are studies suggesting that when meals contain both umami qualities and protein, people are more satisfied following the meal. However, we know that protein tends to provide greater satiety anyway, so it's unclear whether the MSG is contributing to that or if it's just the protein.

To add to the confusion, this same review states that while some earlier studies showed that sweet foods were less satisfying, later studies showed no difference in satiety between sweet and savory foods, nor did either one tend to influence the amount of food eaten over the other one. The 2019 review in Comprehensive Reviews in Food Science and Food Safety mirrors these same findings.

This just highlights the importance of eating a balanced diet, full of a variety of foods, whether you're trying to lose weight or simply maintain where you're at.

The research on MSG is inconclusive but leans toward it being a safe additive to foods. With that said, if you find you experience any symptoms after eating foods with MSG, it might be a good idea to avoid them. Even better, make an appointment with a registered dietitian, who can work with you to help pinpoint the cause of your symptoms.