Monosodium glutamate (MSG), commonly used as a flavor enhancer, has been controversially linked to headaches for decades.
Key Facts:
- Human studies linking MSG to headaches have inconsistent findings, especially when MSG is consumed with food.
- Studies in which MSG reportedly causes headaches often have methodological flaws like inadequate blinding due to MSG’s strong taste.
- MSG intake has a minimal effect on plasma glutamate levels when consumed with food – the mechanism by which many propose it causes headaches.
- Overall evidence does not clearly demonstrate a causal link between MSG and headaches. More rigorous research is needed.
Source: The Journal of Headache and Pain
MSG & Chinese Restaurant Syndrome
MSG is a sodium salt of the amino acid “glutamic acid” used globally as a flavor enhancer.
The so-called “Chinese Restaurant Syndrome” was first described in 1968, linking MSG consumption in Chinese food to symptoms like headaches, numbness, weakness, and palpitations.
Despite numerous human studies since then, there is still debate around whether MSG actually causes these symptoms.
The International Headache Society includes MSG as a headache trigger in their classification system.
However, major food regulatory agencies view MSG as safe due to the lack of rigorous evidence of harm.
This review assessed study quality and tried to determine whether a causal link between MSG and headaches exists.
MSG Studies with Food: No Clear Link to Headaches
Five human studies administered MSG along with food at doses of 1.5-3 grams.
These studies tried to mask the MSG taste by mixing it with foods like juice, rice, and broth.
Overall, there was no statistical difference in headache incidence between MSG and placebo groups in these studies.
One study did find a significantly higher rate of headaches among MSG-treated women.
However, the MSG was poorly masked in a beef broth, raising questions about study blinding.
The review concluded there was no clear evidence linking MSG with headaches when consumed with food, except for this one questionable case.
The doses studied are much higher than typical MSG intake levels.
MSG Studies without Food & Headaches: Contradictory Findings
Seven human studies administered pure MSG dissolved in water, juices or soda at varying doses up to 12 grams without food.
Some major limitations of these studies:
- The high MSG doses often created strong, unpleasant tastes making blinding difficult. This means effects could potentially be psychological due to subjects guessing whether they received MSG.
- Many studies pre-screened for “MSG-sensitive” individuals. This makes results less generalizable to the wider population.
- Small sample sizes limited statistical power.
The results were highly inconsistent across studies:
- 4 studies found significantly increased headaches with MSG vs placebo.
- Doses linked to headaches ranged widely from 2.5-9 grams.
- 3 studies found no difference in headaches between MSG and placebo groups, even at doses up to 12 grams.
Due to significant issues with blinding and contradictory findings in these studies, no clear conclusions can be made about MSG causing headaches without food.
Studies Cited by Headache Classification Guidelines
The International Classification of Headache Disorders lists MSG as a causative headache trigger and cites five human studies as evidence.
However, the systematic review found issues with four of these studies:
- 2 had no statistical analysis performed.
- 1 had incomplete placebo data.
- 1 had no difference in headaches between MSG and placebo.
Only one cited study found increased headaches with higher doses of MSG without food in MSG-sensitive individuals.
But this study may have had blinding issues due to the high MSG doses used.
Overall, the review found that the studies cited as evidence for MSG headaches were inadequate to support a causal link.
MSG Has Little Effect on Plasma Glutamate
Some propose that MSG could trigger headaches by increasing plasma glutamate levels in the bloodstream.
However, research shows MSG intake has minimal influence on plasma glutamate when consumed with food:
- In a study with 6 grams of added MSG at meals, plasma glutamate varied 32-53 μmol/L on MSG days compared to 33-48 μmol/L on non-MSG days – only a 10% difference.
- Plasma glutamate levels normally fluctuate day-to-day anyways.
This provides little mechanistic explanation for MSG in food causing headaches through increased plasma glutamate.
The enhancement of taste when MSG is added to food is thought to come mostly from direct activation of taste receptors in the mouth rather than changes in blood glutamate.
No Strong Evidence that MSG Causes Headaches
Evidence on MSG as a headache trigger in humans is inconsistent and methodologically flawed.
MSG may potentially cause headaches in certain sensitive individuals under fasting conditions with large doses.
But this requires more rigorous confirmation.
MSG as consumed with food at normal dietary intake levels is unlikely to cause headaches based on current evidence.
Mechanistic explanations are lacking for how MSG in food could trigger headaches.
Overall, current evidence does not clearly support a general causal link between MSG in food and headaches.
More properly blinded, placebo-controlled studies are needed to truly determine if MSG is a trigger.
Until then, restrictions of dietary MSG to prevent headaches rest on shaky scientific ground.
References
- Paper: Does monosodium glutamate really cause headache? A systematic review of human studies. (2016)
- Authors: Yoko Obayashi & Yoichi Nagamura