Some people feel lethargic after eating Chinese food which lead to this myth called “Chinese Restaurant Syndrome”. I believe this has to do with the heaviness of the food. I feel the same way whenever I eat rich, heavy, greasy food. Cheap food in general tends to be so, specially cheap Chinese, Indian, and deep-fried food. If you were to stuff yourself with rich French food loaded with butter, cream, and cheese, the same would probably happen but because French food is generally expensive, we don’t stuff ourselves with it. And, that leads to another argument that enhancing the flavors with MSG would be good for us because we would feel more satisfied with less calories.
The main reason why the urban myth of “Chinese Restaurant Syndrome” spread so fast and wide, I believe, is xenophobia. Chinese food was a perfect candidate for it. MSG is strongly associated with Chinese food but it was actually invented in Japan, and the Japanese people probably consume more MSG than the Chinese.