With all the hype surrounding MSG and the horror foodies and nutrition nuts express at the thought of consuming it, you would think that it was a well-established fact that MSG is bad for you. The truth of the matter is that there is no statistical evidence that MSG (monosodium glutamate) actually has a negative impact or that it is significantly unhealthy. 

One study tested multiple people who claimed to be sensitive to MSG. They fasted and then were given one of two pills: a placebo pill with no MSG or a pill with 5g of MSG. They were then given a “standard” breakfast. The experiment was double-blind, which means that neither the testers or the people being tested knew whether the pill was a placebo or not until afterwards. 

Those that received MSG reported no more symptoms than those who received the placebo did. Another similar experiment was done in Geha with 130 people. The study gave similar results. It seems likely that the belief that MSG is bad for you is just the result of anecdote, particularly by Robert Ho Man Kwok who reported symptoms after eating American Chinese food. Maybe it is just an extension of the old health rule: “if it tastes good, spit it out!” 

(Source)