Many people avoid monosodium glutamate (MSG) – the so-called “safe” flavor enhancer – because they get a headache or upset stomach after eating it. But here’s another reason to avoid MSG: It might be causing you to gain weight.

MSG has been used for some time to “fatten up” lab rats for experimental purposes – but no one knew for sure if it had the same effect on people. So researchers from the University of North Carolina at Chapel Hill and in China set out to study just that.

The researchers compared the MSG consumption of more than 750 Chinese men and women aged 40 to 59. (In China, MSG is commonly used in home cooking, as well as in restaurants and packaged foods. And, in fact, the study found that approximately 82 percent of the subjects used MSG when they prepared food at home.) Those who consumed the most MSG were almost three times as likely to be overweight as compared to those who did not use MSG, even when adjustments were made for physical activity, caloric intake, and other variables that could be related to weight gain.

The researchers are now trying to determine why MSG causes weight gain. One theory is based on the observation that when lab rats are given MSG, they eat more, indicating that MSG somehow influences appetite signals from the brain.

Another concern is the way MSG affects blood sugar. In a 2000 study published in the journal Physiological Research, normal rats were turned into insulin resistant rats by feeding them MSG. The MSG-treated rats also stored glucose as fat more readily than normal rats.

Whatever the reason, it appears that one way to help control your weight is to reduce your intake of MSG.

In the U.S., most people do not use MSG in home cooking, though it is an ingredient in the flavor enhancer Accent. You are more likely to get MSG in restaurant food. You can’t control the way food is prepared when you eat out, but you can at least make sure you read the labels when you shop at the grocery store. Foods to watch out for include soups (especially Asian-noodle type soups) and salad dressings. Many flavor-coated foods – like ranch or barbeque flavored chips and nuts – also contain a significant amount of MSG.

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