Is the MSC Associated with Any Physical Symptoms?

The MSC usually occurs when a fairly large amount of MSG is consumed on an empty stomach in a broth or soup at an Oriental restaurant. Typically at least 3-5g of MSG must be consumed within short period of time to trigger the MSC. However, even in people who react consistently to MSG in a liquid the same amount of MSG consumed with solid food does not usually elicit the same reaction or any reaction at all in most cases. Under controlled conditions no objective changes in blood chemistry (except for a transient rise in GLU levels), blood pressure, skin temperature, etc. have been observed while people are experiencing these symptoms.

So while the symptoms of MSC are clearly felt by many people there are no accompanying physical changes in the body that can be measured objectively to verify the presence of such symptoms.

The MSC can be triggered in perhaps 30% of Americans who consumed at least one to two tsp. (3-6g) of MSG in a broth-type soup or other liquid on an empty stomach. Even under these circumstances the consumption of less than 2-3g of MSG is usually insufficient to create MSC symptoms in nearly all people who report having experienced the MSC in the past. It should be noted that more than 1g of MSG per serving in tomato juice or soup does not usually improve overall palatability. Therefore, the amount of MSG needed to maximally enhance flavor and sensory pleasure is well below the threshold for triggering the MSC in nearly all people. The consumption of a high carbohydrate food before or with the MSG usually blocks the MSC in susceptible individuals. If MSG is used in moderation and consumed with some carbohydrate-rich food then it seems unlikely that MSG will cause any physiological or psychological changes in the body.

(Source: http://www.foodandhealth.com/cpecourses/msg.php#_Toc508575087)