Although these worries surface periodically on the Internet, the answers seem to be, “yes, it’s safe,” and “no, it’s not causing obesity.”
The US Food and Drug Administration has declared MSG, or monosodium glutamate, safe for most people when it is consumed in standard doses, though some people do have short term reactions such as numbness, burning, tingling, facial pressure or tightness, chest pain, headache or nausea. A typical serving of glutamate-treated food contains less than 0.5 grams of MSG; a large serving, which is more likely to provoke a reaction, would be three grams or more. MSG is more likely to provoke a reaction if consumed on an empty stomach. People with severe, poorly-controlled asthma may also be more likely than others to have a reaction to MSG.
As for the obesity question, that’s a bit murky. There is evidence (look under “MSG obese” on www.pubmed.gov) that researchers can induce obesity by giving animals MSG. “But to blame the obesity epidemic on MSG? That’s stretching it,” said Amy Campbell [cq], a dietitian at the Joslin Diabetes Center. “I’m not saying there isn’t a potential link, but given that this research has been going on since the 70s, if there truly were a connection, we’d know by now.”
Dr. George Pauli, associate director for science and policy in the FDA’s office of food additive safety, said in an email, “I can see no link with obesity unless making food taste better leads to eating more.”
Campbell summarized things this way: “There is a gap in what we know about MSG and its effects. So it’s not a bad idea to go easy on it. But don’t make yourself crazy trying to avoid it. We have other, more important, things to worry about – like trans fats and saturated fat in the diet.”