NEW YORK (Reuters Health) – Eating foods that contain lots of monosodium glutamate (MSG), a flavor enhancer frequently used in Asian cuisine, can make you fat, new research published in the journal Obesity suggests.

Rural Chinese men and women who consumed the most MSG were more than twice as likely to be overweight than their peers who didn’t use the additive, Dr. Ka He of the University of North Carolina at Chapel Hill and colleagues found.

In 1969, He and his team note in their report, a study showed that mice given large doses of MSG shortly after birth had gained more weight by 4 months of age than control mice, even though the control animals ate more. Researchers have also spotted injuries in the hypothalamus, a part of the brain that helps regulate appetite and fat metabolism, in mice given MSG.

But to date no one has investigated whether MSG intake is associated with weight gain in humans, according to He’s group, possibly because intake of the additive from processed foods is difficult to measure. To fill in this knowledge gap, the researchers analyzed data from the International Study of Macro-/Micro-nutrients and Blood Pressure (INTERMAP), an investigation conducted to examine the relationship between sodium and blood pressure.

The study included 752 healthy men and women living in three different rural Chinese villages. All ate very little processed food, making it easier for researchers to estimate MSG intake by looking at how much the study participants used when they prepared their meals.

The researchers found that 82.4 percent of study participants used MSG, with an average intake of 0.33 grams per day. Average body mass index (BMI) for non-MSG users was 22.3, compared to 23.5 for people who consumed the most MSG.

Once the researchers adjusted the data for the affects of physical activity and the total amount of calories consumed, they found that individuals in the top third of MSG consumption were 2.1-times more likely to have a BMI of 23 or higher than non-users. A BMI of 23 is considered overweight for Asian populations by the World Health Organization.

The heaviest consumers of MSG were 2.75-times more likely than non-users to have BMIs of 25 or greater, the international standard for overweight. The relationship was seen for both men and women.

Almost all research in animals linking MSG to hypothalamic damage has looked at the results of injecting the substance, rather than ingesting it, and the issue of whether the additive actually causes such damage is still being debated, He and colleagues note.

“Nevertheless,” they add, “the findings from our study support the judgment against MSG supplementation of human foods.”

SOURCE: Obesity, August 2008.