For reasons that are not entirely clear, subsequent attention zeroed in only on the possible role of MSG. Kwok's symptoms were subsequently dubbed ''Chinese Restaurant Syndrome'' by the journal and, by 1969, the finger had been pointed unequivocally at MSG. Go natural ... chef Dan Hong with kombu, a seaweed that contains naturally occurring glutamates. Credit:Marco Del Grande Since then, few food ingredients have been more extensively studied, vilified and defended as MSG. But it is hardly a new phenomenon. In fact, MSG has effectively been part of Japanese cooking for centuries in the form of kombu, a type of seaweed that is a key ingredient of dashi soup stock. Traditional Japanese chefs knew the stock had a unique property - it brought out the savoury flavour of other ingredients. And then, in 1908, University of Tokyo chemist Kikunae Ikeda isolated the unique flavour of kombu.

Ikeda reasoned kombu's flavour, and the flavour it revealed in other ingredients, was neither sweet, salty, sour or bitter - he coined the word ''umami'' to describe it. Ikeda went further, identifying the key element of the seaweed, which turned out to be a common amino acid called glutamic acid. He stabilised the substance with ordinary salt and thus monosodium glutamate was born. He patented his discovery and MSG began to be produced on a commercial scale (by fermentation) and used to enhance the flavour of practically every processed food you can name. We can't get enough of it - it's like catnip for humans. In fact, there is now growing evidence we have taste receptors that are naturally programmed to relish glutamate. And glutamate occurs naturally everywhere in our diets. Ripe tomatoes are full of it, as are dried mushrooms and broccoli. Parmesan cheese, in particular, is loaded with the stuff, which is why it is such a popular addition to meaty sauces like ragu bolognese. It even occurs in human breast milk.

The overwhelming evidence from a large number of scientific studies is that MSG is safe for the general population in the levels typically found in food. Since Kwok put pen to paper about his symptoms, there have been hundreds of studies that have looked at possible links between MSG and the reaction he and others described. In 1988, the World Health Organization and the United Nations reviewed all the evidence and concluded that MSG ''did not represent a hazard to health''. Then, in 1995, the US Food and Drug Administration did its own review and found that high levels of MSG had no effect on most people. There is a small group of people who show some response - but only after taking a massive MSG pill on an empty stomach. In his book It Must've Been Something I Ate, American food writer and iconoclast Jeffrey Steingarten asks why, if MSG is eaten daily by billions of Chinese, they don't all have a headache. But none of this has quelled persistent claims linking MSG with everything from diabetes and autism to Alzheimer's and heart attack. Sites such as banmsgnow .info and msgtruth.org routinely allege there is a conspiracy from ''Big Food'' to poison us with MSG. Among the more hysterical claims are that MSG can cause brain damage in humans and a small amount is sufficient to kill a dog.

At least part of the reason behind this hysteria lies in the fact that many reported symptoms are totally subjective. If someone complains of ''general weakness'' it is all but impossible to test that objectively. Designing studies that isolate the effects of one compound in our diet is also difficult. ''With any epidemiological study there are a lot of complexities in measuring food intake,'' a biomedical research scientist at the University of Adelaide, Natalie Luscombe-Marsh, says. ''If you don't take into account … other parameters like other nutrients and people's dietary patterns you get these different results. ''There is really no experimental evidence to substantiate Chinese Restaurant Syndrome or links with asthma but that doesn't preclude that there is definitely a small percentage … who would be truly sensitive to MSG. But the majority of the bad press is unsubstantiated.'' Food Standards Australia New Zealand has reviewed all the evidence and come to the same conclusion. ''The overwhelming evidence from a large number of scientific studies is that MSG is safe for the general population in the levels typically found in food,'' a spokeswoman for FSANZ, Lorraine Belanger, says. ''A small number of people may experience a reaction … but there's no convincing evidence that MSG is responsible for more serious effects like those you might see in an allergic response to things like peanuts.'' MSG, EASY AS 1, 2, 3

AUSTRALIAN food manufacturers must list added MSG on their labels, either by name or with the food additive code 621. Other glutamates have the numbers 622 to 625. Restaurants are not required to disclose whether they use MSG. The advice from the NSW Food Authority is to ask, if you believe you are sensitive. ''Sensitive individuals should also be aware that high amounts of glutamates maybe be present naturally in certain food,'' the advice says. Foods that are naturally high in glutamates include soy sauce and Vegemite. Dan Hong, the head chef at Ms.G's, the cheekily named modern Asian restaurant in Potts Point with a menu that ranges from Vietnam to Korea and China, says for Chinese food in particular MSG ''is part of the repertoire''. ''It's a tradition that goes back hundreds of years,'' he says. In spite of the restaurant's name, Hong doesn't use powdered MSG in his cooking. ''We try and use natural forms of MSG like kombu and stuff like that,'' he says.

Kombu has been in the news not for the glutamate it contains but its iodine content. Iodine is an essential nutrient but for a small proportion of the population, excessive iodine can be a problem. Since last October, quarantine authorities have rejected kombu from Korea, China and Japan that has more than 1000 milligrams of iodine per kilogram.