MSG and Allergy: Science Looking for a Culprit for Over 40 Years

By A Reis

In 1968, the New England Journal of Medicine received a letter from scientist Robert Kwok describing a series of symptoms experienced by himself every time he had a meal at a Chinese restaurant. Fittingly, he named it “Chinese restaurant syndrome”. The syndrome, he explained, usually begins 15-20 minutes after ingesting the food and lasts for about 2 hours, with no lasting effects afterwards. In his letter, he suggested several potential culprits including wine and excesse salt, but for some reason, it was his suggestion that it could be the glutamate added as a flavour-enhancer additive that caught the attention of scientists.

Since then, science has been looking for a mechanism to explain such syndrome for over 40 years, but so far it hasn’t even been able to determine convincingly whether glutamate is to blame or not. In fact, double-blind tests of individuals who claim to suffer from this ‘syndrome’ have failed to confirm the role of glutamate as the provocative agent, raising the question of the validity of such syndrome.

Monosodium glutamate (MSG) is naturally found in all foods, from meat and fish, to vegetables and fruit. Also, with a quick search through your cupboards, you’ll find it present in most processed foods as well, such as sauces and pre-prepared meals. This is because it was discovered over 100 years ago by Professor Kidunae Ikeda that adding it to food would enhance its flavour by stimulating a specific taste that Prof. Ikeda called unami, to add to sweet, sour, bitter and salty that were already known. Unami can be roughly translated from Japanese as “savoury deliciousness”.

Certainly you cannot avoid MSG in what you eat, and it is in fact a vital part of our metabolism, with essential functions. Dietary glutamate is absorbed by an active transport system into intestinal cells where is used to produce energy, and very little actually reaches the blood supply. Plasma levels are only significantly affected when large doses of glutamate are ingested at the same meal, but levels return to normal within 2 hours, and 99% of the population is not affected by this transient increase. Inexplicably it seems to elicit a reaction in about 1 in 100 people, causing burning sensations in the back of the neck and chest, facial tightness, chest pain, headache, nausea, palpitation, numbness in back of the neck radiating to arms, tingling, warmth, weakness in the face and upper back, drowsiness and generalised weakness.

Although based more on the sheer number of people complaining of such symptoms rather than scientific studies conducted to test the impact of MSG, the current theory defends that its consumption can cause a reaction, but only in a very small subset of the general population and only when done excessively at the same meal (more than 5g, Walker and Lupien, 2000). This is why it only occurs after restaurant or highly processed meals and not if you chose foods with naturally occurring glutamate. You would need to eat over 2,5kg of peas or over 16Kg of carrots in one go to consume that amount of glutamate! In contrast, one meal at a Chinese restaurant can have more than the required amount to provoke a reaction.

At a first glance, given the immediate appearance of symptoms, you could be fooled in thinking that it is a simple allergic reaction to MSG. However, Pulce et al. (1992) found no evidence of an IgE-mediated response, indicating that the Chinese restaurant syndrome cannot be considered a real allergy. It could, at best, be classed as a food intolerance, which doesn’t evoke the same immunological responses. However, to date, no further studies really address this issue with the objective of determining exactly the mechanisms behind the Chinese restaurant syndrome.

On this occasion science hasn’t been able to reach a conclusion and the debate continues. It is currently assumed that MSG is safe for human consumption without any specific maximum levels, with the proviso that about 1 in 100 people may experience some discomfort after eating food rich in MSG. It may be uncomfortable if you’re that 1 and you need to avoid your local Chinese restaurant, but science seems to have lost interest in this question and now all that is left is a myriad of articles online defending both camps, but no way to decide which one is right. Google MSG and you’ll find it blamed for anything from migraines to depression, or called a miraculous component that is “natural, tasty and safe” depending on which side of the fence you land. It’s up to you to make up your mind!

References

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