MSG and obesity?

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Why are we fat? No no no no! Not that stuff about eating-too-much-and-moving-too-little. We’re talking about all the other theories out there -- we examined a slew of them recently in a Health section article by Karen Ravn. Stuff like corn syrup, obesity viruses, etc.

Here’s one I hadn’t heard of before (though it appears I have been living in a cave): too much MSG (monosodium glutamate). A study just published in the journal Obesity reported that people who use MSG to enhance the flavor of their foods are more likely to be obese than those who don’t.

Conducted by Dr. Ka He of the University of North Carolina at Chapel Hill and coworkers, it looked at 750 Chinese men ages 40 to 59 in three rural villages. Most of the people in the study ate their food at home and 82% of them added MSG to it. Participants were divided into groups based on the MSG quantities they said they consumed, and obesity rates determined. The prevalence of obesity in the one-third eating the most MSG was almost three times that in the group that ate no MSG. The researchers say they controlled for factors such as overall calorie intake and levels of physical activity, and that an MSG link is supported by some earlier animal studies.

I’d love to direct you to a place online where you can read the study for free, but alas, Obesity -- like most medical journals -- doesn’t permit that. You just get a synopsis. But you can read about it here.

I e-mailed the first author Ka He about the study -- see (edited) questions and answers below.

ME: If I were to cite the most important studies done previously in animals linking MSG to obesity, which would they be?

KH: You can cite Dr. John Olney’s study, which was published in Science in 1969. [I dug around on the Web a little bit and found a few interesting documents on the issue when it first came out, including this editorial in the Washington Post. Olney, according to that Washington Post editorial, ‘reported that newborn mice suffered specific brain damage from injection with a very large dose of MSG, a level that would be equivalent to 35 grams in the adult. Subsequent rats, rabbits and one monkey were reported to show similar responses, mainly in the hypothalamus -- a part of the brain concerned with the regulation of hormones, of temperature, and of body weight.... However, so long as only modest amounts of MSG are used, small in relation to the glutamic acid normally furnished by the rest of the
diet, it is hard to see any basis of concern.’]

ME: What mechanism do you believe lies behind an MSG-obesity link?

KH: Animal studies suggest that MSG intake may induce hypothalamic lesions and leptin resistance, possibly influencing energy balance, leading to overweight. Certainly, we need further studies to elucidate the potential mechanisms. [Note: Leptin is a body chemical that suppresses appetite.]

ME: Do you think it’s a major contributor or a minor contributor to the rising rates of obesity in this country? How big a contribution do you think it might make?

KH: This is a difficult question. Frankly, I do not think we can answer it with the current data. Our body weight is determined by our lifestyle but not a single factor. But, it will be very important and significant at the population level even if we just eliminate a ‘minor’ risk factor of obesity.

ME: How much MSG do we eat in this country? I know that some Chinese cooking has contained a fair amount, but what about the Western world, and have those trends changed much?

KH: When we talk about MSG, most people will immediately think about Chinese food. It is true that MSG is very common in Chinese food. But, not many people know that worldwide MSG consumption including that in Western countries has increased dramatically in recent decades. The secret is that MSG has many hidden names. For example, some seasonings may contain substantial amount of MSG. You may find some relevant information in an article published in New York Time on 03/05/2008.

Here are some other interesting MSG links:

That (excellent) New York Times article Ka He recommends -- it goes into all kinds of MSG trivia and history, including periodic safety controversies and scientific reviews. (It notes that most scientific reviews have judged MSG to be safe.)

From the Food and Drug Administration, also citing various reports that have indicated that MSG is safe.

From Wikipedia, lots of MSG stuff and another page discussing rodent-obesity studies and safety investigations.

MSG? Obesity? Truly? Seems there’s been an avalanch of recent reports suggesting odd associations with traits you wouldn’t expect to be linked to obesity. Kids’ ear infections. Physical coordination in childhood. What to make of these things? Studies often may be unable to distinguish cause from effect. Some associations may be real, others may be spurious. Some traits may be directly linked, while some serve as ‘markers’ for other traits (if someone found that ketchup consumption was linked to obesity, for example, the culprit might not be the ketchup but the types of foods you put ketchup on). Taking coordination, for example, you could construct a good, just-so story along these lines: Kids are less coordinated because they’re less physically active and thus don’t develop coordination skills as quickly. That relative physical inactivity also eventually leads to more weight gain.

Finally, talking of MSG, my brother Ben used to make this dish when we were latch-key teenagers. We had it often for dinner.

1) Boil white rice. 2) Drain. 3) Dab with butter. 4) Sprinkle with MSG. 5) Serve. 6) Enjoy!

I haven’t eaten it recently -- but concern for my weight has not been the principal reason why.

-- Rosie Mestel