Is MSG (E621) bad for you?
Monosodium glutamate (E621) is the sodium salt of glutamic acid, an amino acid naturally abundant in parmesan, tomatoes, mushrooms and breast milk. Double-blind trials have not reliably reproduced the reported symptom cluster at normal dietary levels. EFSA and the FDA both consider it safe as used.
What MSG is
Glutamic acid is one of the most common amino acids in nature. Monosodium glutamate is simply its sodium salt, the form that dissolves easily and delivers umami, the savoury fifth taste identified by Kikunae Ikeda in 1908.
Your body cannot distinguish glutamate from MSG from glutamate in a tomato. It is the same molecule, metabolised the same way.
Naturally high-glutamate foods include parmesan (very high), tomatoes, mushrooms, soy sauce, fish sauce, Marmite, walnuts, peas and human breast milk. Nobody has ever campaigned against parmesan.
Where the reputation came from
In 1968 the New England Journal of Medicine published a letter from Dr Robert Ho Man Kwok describing numbness, weakness and palpitations after eating at Chinese restaurants. He speculated about several causes, including cooking wine, sodium content and MSG.
The press seized on MSG. The phrase "Chinese restaurant syndrome" entered the language and stayed for fifty years. The obvious point should be named: the same additive was, and is, used throughout the Western processed food industry, in crisps, stock cubes, instant noodles and ready meals, without ever attracting a comparable panic. The scrutiny attached itself to a cuisine rather than a molecule.
What controlled studies found
Decades of double-blind, placebo-controlled research have consistently failed to reproduce a specific MSG symptom complex at normal dietary levels. Where studies gave very large doses on an empty stomach without food, a small number of sensitive individuals reported transient symptoms, but the effect did not reproduce reliably when MSG was given with food, as it always is in real life.
Both EFSA and the FDA classify MSG as safe as used. EFSA's 2017 re-evaluation did establish a group acceptable daily intake for glutamates, noting that some population groups may exceed it. That is useful to know, and a long way from the reputation.
So should you ignore it entirely?
Two honest caveats.
Individual sensitivity exists. Some people report a consistent, repeatable reaction. Population-level evidence not finding an effect does not mean no individual has one. If you consistently react, avoid it. You do not need a study's permission.
MSG is a marker of processing. Products containing MSG tend to be highly processed: crisps, instant noodles, stock cubes, ready meals. If avoiding MSG has made you feel better, the plausible mechanism is the change in overall diet, not the molecule itself.
The hidden-name problem
If you do avoid it, be aware that glutamate appears under many names, and some products advertising "no MSG" contain glutamate from other sources:
- Monosodium glutamate, E621
- Monopotassium glutamate (E622), calcium diglutamate (E623)
- Hydrolysed vegetable protein
- Autolysed yeast extract, yeast extract
- Soy protein isolate
- Natural flavouring, in some formulations
Yeast extract is the notable one. It is naturally rich in glutamate and is widely used in products marketed as free from artificial additives. "No added MSG" and "no glutamate" are entirely different claims.
MSG is one of the most studied food additives in existence and the evidence for population-level harm is weak. If you react to it, avoid it. If you do not, avoiding it is not buying you health, and the products it appears in may still be a good idea to eat less of, for reasons that have nothing to do with E621.
Frequently asked
Does MSG cause headaches?
Controlled double-blind studies have not reliably reproduced headaches at normal dietary levels. Very high doses given without food have produced transient symptoms in a minority of people. Some individuals report a consistent personal reaction, which deserves respect without being generalised.
What is E621 in food?
E621 is monosodium glutamate, the sodium salt of glutamic acid, used as a flavour enhancer for umami. It is chemically identical to glutamate occurring naturally in parmesan, tomatoes and mushrooms.