Monosodium glutamate: MSG, a sodium salt of the amino acid glutamic acid that enhances the flavor of certain foods. Originally isolated from seaweed, MSG is now made by fermenting corn, potatoes and rice. It does not enhance the four basic tastes (bitter, salty, sour, sweet) but it does enhance the complex flavors of meat, poultry, seafood, and vegetables. MSG is an important ingredient in the cuisines of China and Japan and is used commercially worldwide in many types of foods. It is naturally present at high levels in tomatoes and Parmesan cheese. In China, MSG is known as wei jing, which means flavor essence.
The Chinese restaurant syndrome was first described in 1968 in people who had eaten Chinese food on which MSG had been lavished. The syndrome only seems to occur in some people. Their symptoms may include headache, throbbing of the head, dizziness, lightheadedness, a feeling of facial pressure, tightness of the jaw, burning or tingling sensations over parts of the body, chest pain, and back pain. Large amounts of MSG may cause arterial dilatation (widening of arteries). Many Chinese do not believe in the existence of the Chinese restaurant syndrome. It may be a hypersensitive (allergic) reaction.