Some researchers contend this food habit helped influence the decline the Roman Empire. Here’s a balanced look at MSG from Esther Inglis-Arkell on io9.com:
Monosodium glutamate is a food additive that enhances flavor. Although it’s frowned upon today, the ancient Romans loved it and ate it with almost every meal.
There’s been some debate over what exactly monosodium glutamate does to people. Some people say it gives them severe headaches, numbness, weakness, and even heart palpitations. Scientists could confirm that it does give some people short-lived reactions, but no tests showed that it had long-term health effects. Some say that it’s an addictive substance which causes people to crave it repeatedly if they try it too often. Others say it’s just a flavor enhancer, and people crave it because it makes things taste better.
The chemical is listed as ‘safe’ by the FDA, although they do require it to be clearly listed as an additive in any food product that uses it.