Monosodium glutamate is the sodium salt of glutamic acid. Glutamate is a naturally occurring amino acid that is found in nearly all foods, especially high protein foods such as dairy products, meat and fish and in many vegetables. Foods often used for their flavoring properties, such as mushrooms and tomatoes, have high levels of naturally occurring glutamate. The human body also produces glutamate and it plays an essential role in normal body functioning.

Monosodium glutamate added to foods produces a flavoring function similar to the glutamate that occurs naturally in foods. It acts as a flavor enhancer and adds a fifth taste, called "umami," which is best described as a savory, broth-like or meaty taste.

Despite a small number of persons reporting sensitivity to monosodium glutamate, scientific studies have not shown any direct link between monosodium glutamate and adverse reactions in humans. Monosodium glutamate used to be blamed for the "Chinese Restaurant Syndrome" because the first anecdotal report was made following consumption of a Chinese meal and monosodium glutamate is widely used in Asian cooking.

Symptoms said to be experienced included burning sensations along the back of the neck, chest tightness, nausea and sweating. However, a double-blind controlled challenge of individuals claiming to suffer from the "syndrome" failed to confirm monosodium glutamate as the causative agent. Other studies have found that allergic-type reactions after Asian meals are more often due to other ingredients such as shrimp, peanuts, spices and herbs.

Children metabolise glutamate in the same way that adults do and monosodium glutamate is safe for children. In fact, human breast milk contains 10 times more glutamate than cow's milk.