M-S-G is the abbreviation for 'monosodium glutamate' (MON-uh-so-dee-um GLUE-tuh-mate). It's a form of glutamic (glue-TAM-ick) acid, one of the amino acids that help build proteins. It's found naturally in foods such as mushrooms and tomatoes, where it's bound to other compounds. The free form of glutamate is added to processed foods, such as packaged soups, sauces, and frozen dinners. Food labels also may refer to it as 'hydrolyzed food starch' or 'hydrolyzed plant protein.' Although M-S-G is termed by some as a 'flavor enhancer,' its real effect is to stimulate the nervous system to increase sensitivity to a food's taste. Although the U-S Food and Drug Administration, the National Academy of Sciences, and the World Health Organization have concluded it doesn't cause any long-term medical problems, anecdotal evidence supports that the food additive can cause reactions in some people. Some symptoms include numbness in the extremities, mild to severe headaches, heart palpitations, chest pain, nausea, asthma attacks, and a dry mouth. It also may affect mood and emotions, causing irritability and depression.