Monosodium glutamate, abbreviated as MSG, is a flavor enhancer found in a lot of processed foods.
This additive (E number E621), is the sodium salt of a non-essential amino acid called glutamic acid. Chemically, MSG is a white crystalline powder that closely resembles table salt. Current data suggests the average daily intake of MSG in modernized countries is 0.5-2.0 grams per day.
The substance is commonly associated with food in Chinese restaurants due to the historical occurrence of “Chinese Restaurant Syndrome” in 1968, where a man named Robert Ho Man Kwok reported symptoms of numbness, general weakness, and heart palpitations after his meal.
The controversy for using MSG in food products has continued to be questioned ever since in scientific and health communities.
The Potential Negative Effects of MSG
1. May Cause Headaches
Glutamic acid functions as an excitatory neurotransmitter in the brain that stimulates nerve cells, however some reports claim that MSG leads to excessive glutamate storage. In turn, it has been linked with an overstimulation of nerve cells.
For this reason, MSG has been labeled as an excitotoxin.
Various studies have confirmed the link between MSG and side effects such as intense headaches, seemingly occurring within 30 minutes when a single oral dose surpasses 3 grams .
Removal studies also confirm that the elimination of MSG from the diet decreases the frequency of headaches .
Mechanistically, although the blood brain barrier has a low permeability to MSG, the presence of glutamate transporters located at the barrier could facilitate the uptake of MSG into the brain.
Based on assumptions that ~10% of MSG in the blood can reach the cerebral spinal fluid, this would make it physiologically possible that MSG concentration in the brain can go above the threshold thought to cause neuronal injury; ∼3 µM . However, keep in mind that 3 grams is a very high dose — about six times the average daily intake in adults .
Human studies showing MSG causes headaches are not consistent, and this could be for a number of reasons.
Firstly, a report on children noted that they do not experience the side effects from MSG. To add to this, MSG is commonly added to dishes in China, yet this population has not been noted to have an issue with this chemical or headaches.
It is theorized that only mature neurons are susceptible to damage from MSG, and due to this young children that only have immature neurons do not experience headaches.
In addition, it has been demonstrated that pre-treatment of neurons with a low dose of MSG can make neurons tolerant to future doses of MSG. The finding may explain why Chinese populations do not experience headaches after MSG intake, as they may have established previous exposures to low doses of MSG when they were young .
Another explanation for the inconsistent results could be because most studies do not properly blind their subjects from MSG intake – as it is extremely sweet – so subjects may be aware they are consuming MSG and then expect a headache to occur . These events may influence the occurrence of headache quite strongly especially in case of migrainers and subjects who believe they are MSG-sensitive.
2. May Develop Metabolic Syndrome
Metabolic syndrome is the medical term for a combination of diabetes, high blood pressure and obesity.
Animal studies also support a causative relationship between obesity and high doses of MSG, possibly by acting on immature neurological mechanisms that regulate food intake and energy expenditure .
Alternatively, MSG may enhance the amount of dietary glucose that is shifted towards fat synthesis by activating the gene expression of enzymes involved in lipid biosynthesis and storage in adipose tissue .
In rural human populations, there are also significant associations between daily MSG intake and the risk of the metabolic syndrome, and this association is independent from major confounding factors such as age, sex, smoking, family history, physical activity, and calorie intake .
There is even available research that links MSG intake to an increased risk of obesity in humans, independent of physical activity and total energy intake .
Some evidence suggests that despite significant trends for increasing MSG consumption and increased risks for metabolic syndrome, this relationship in most cases becomes insignificant when accounting for confounding factors such as sex, age, calories intake, physical activity, smoking status, and diabetes history .
Interestingly, some studies even suggest that MSG could help with obesity, as people who consume soups flavored with MSG actually eat less calories at subsequent meals – especially in the form of added sugar . This may indicate that MSG triggers the release of appetite-regulating hormones that decrease daily caloric intake.
More data is needed to clarify whether MSG causes metabolic syndrome.
What Do Health Organizations Say About MSG?
The U.S. Food and Drug Administration has generally recognized MSG as being safe to consume – especially at the levels consumed by the general population .
This is because the natural level of glutamic acid in foods, and the amount used as additives, is not significant enough to be a toxicological concerns in humans .
However, even health organizations are not making conclusive statements regarding MSG, as more human research is necessary to fully understand its metabolic effects.
The safety of MSG largely depends on its dose, and the sensitivity of the individual consuming it. Therefore, the product cannot be labelled either “safe” or “dangerous” without taking other factors into context.
MSG is safe in moderate amounts, however consuming far beyond the average daily amount can potentially cause headaches and metabolic syndrome.
Individuals should assess their tolerability to MSG, and remove it from their diet if side effects are noted. On the other hand, if no side effects are experienced, there is no scientific reason to remove MSG from the diet.
However, keep in mind that MSG should not be a cause for concern if people are consuming balanced whole-food diets, because MSG is generally found in processed foods.