The most common reaction to MSG and to aspartame is migraine headache. MSG-sensitive people react to glutamic acid that has been freed from protein through a manufacturing process. We are well aware of celiac sprue. Gluten is not MSG, but many individuals with celiac sprue have suffered reactions from processed food that they thought was free of gluten. Congress has passed legislation that has allowed food processors to treat the ingredients of flavorings as proprietary information, and FDA regulations allows hydrolyzed proteins, including hydrolyzed grains, to be included in flavorings.
Grains are high in glutamic acid.
One final point. People afflicted with celiac sprue vary in their tolerance for grains. Therefore, not all people with celiac sprue react to all flavorings that include grain. The symptoms of fibromyalgia, as Rich stated, are the symptoms associated with aspartame ingestion, but are also the symptoms associated with MSG ingestion. Last week, I spoke with a retired physician in Ohio who told me that he cured his fibromyalgia by elimination of MSG, and cured 57 patients in his practice who had been diagnosed as suffering from fibromyalgia with the same approach.