MSG (short for monosodium glutamate) is a type of flavouring added to some pre-packaged foods, such as soups, canned vegetables, and processed meats. People also add it to enhance the flavour of foods such as poultry, seafood, and vegetable dishes. It is also a popular ingredient in Chinese cuisine.

Glutamates are naturally occurring amino acids that are present in protein-rich foods. If you eat mushrooms, fish, seaweed, tomatoes, or certain types of cheese, you're likely ingesting some amount of natural glutamate. MSG is the sodium salt of glutamate, consisting of glutamate, sodium, and water.

Both glutamates and MSG possess a unique flavour many find quite pleasing. It's not sweet, not sour, not bitter, and not salty. It's actually umami, the elusive "fifth taste" that many researchers believe our tongue is especially designed to taste. Umami could be described as savoury, broth-like, and somewhat meaty.

Why does MSG have a negative reputation?

Soon after dining at a Chinese restaurant back in 1968, Dr. Robert Ho Man Kwok experienced a cluster of physical symptoms, notably numbness in his neck and a sense of pressure in his face and upper chest muscles. He dubbed his symptoms "Chinese Restaurant Syndrome" (CRS).

Since then, many people have described these and other symptoms - flushing, headache, sweating - after eating foods containing MSG. CRS has gone by several other names: hot dog headache, glutamate-induced asthma, MSG Symptom Complex, and MSG syndrome, to name a few.

Whatever it is called, post-MSG symptoms are rarely serious and usually go away without requiring treatment. If symptoms escalate to serious chest pain, heart palpitations, shortness or breath, or a swelling of the throat, immediate medical attention should be sought.

So, is MSG safe?

Over the years, extensive research has failed to establish a definite link between MSG and these symptoms. The World Health Organization deemed the flavouring safe for consumption.

Concerns that MSG could be unsafe for infants and pregnant or nursing women were also disproved. As it turns out, babies metabolize glutamate the same way adults do, and it cannot pass through the placental barrier to affect a developing fetus.

What can I do if I'm sensitive to MSG?

Despite the safety assurances, there are people who are sensitive to MSG. Eating foods containing the flavouring may trigger a hypersensitive reaction or allergic-type reactions in some (even though MSG is not considered an allergen).

For that reason, Health Canada and the U.S. Food and Drug Administration both require that MSG be listed on food labels when it is added as an ingredient. It cannot be hidden behind ambiguous names like "spices" or "natural flavouring."

No limit has been set on how much MSG can be added to food, but Health Canada says that it should be added at levels consistent with Good Manufacturing Practice. This means that MSG should be added in the smallest possible amount needed to enhance flavour.

So, if you have experienced post-MSG reactions, check food labels and, when you dine out, ask about the MSG content of restaurant meals.

What about the rumours that MSG makes you fat?

There is no clear scientific evidence leading to the conclusion that consuming MSG-containing foods causes obesity in humans. However, scientists continually examine the effects of MSG.

A 2008 study observed that consuming MSG may be linked with an increased risk of being overweight. Sparked by animal studies that showed a link between MSG and excess weight gain, scientists at the University of North Carolina decided to track its effects on human obesity. Researchers chose to look at 752 healthy Chinese people living in rural villages, since much of their diet consisted of fresh, unprocessed food prepared at home.

What researchers noticed was that obesity was much more common among those villagers who added MSG to their food than among those who avoided the flavouring. This correlation persisted even after ruling out other reasons for weight differences, like how active villagers were or how many calories they consumed daily. The study is far from conclusive, and shows a correlation, not a causation (it may be, for instance, that those more prone to obesity were also more prone to dietary habits that included adding MSG), but it may continue to add to the controversy of MSG.

Amy Toffelmire