Monosodium Glutamate is added to many foods that are commonly eaten. Be sure to read the labels on the foods that you purchase to be aware of what is being added to it. MSG is an excitotoxin and is added as a flavor enhancer but has been connected to migraines and other diseases that we commonly see today.
It is not always labeled monosodium glutamate or even MSG. It may be listed as hydrolyzed protein, textured protein or many other names.
A good list of different names that it may be hidden as can be found at the website of the Food Renegade. Check it out. http://www.foodrenegade.com/msg-dangerous-science/
A way to know that you are not getting this additive is to stay away from processed foods. Eat real foods the way that nature grows them.