Population study links MSG to increased rates of overweight and obesity; outcome affirms disturbing results from many animal studies
by Craig Weatherby
The U.S. Food and Drug Administration and the World Health Organization agree that MSG (monosodium glutamate) does not pose a health hazard to humans.
Their reassurances relate to ongoing reports that MSG causes acute, allergy-like reactions in a small percentage of people… and to fears that MSG could cause brain damage, especially in young children.
While individuals may experience unusual reactions to MSG, fears about brain damage appear exaggerated and remain unsubstantiated.
But disturbing new findings suggest that dietary MSG could be driving the world's fast-growing, intertwined pandemics of obesity and diabetes.
Accordingly, the new findings call public health agencies' bland reassurances about MSG into question.
The results of a joint U.S.-Chinese epidemiological study indicate that people who add MSG (monosodium glutamate) to their food are more likely to be overweight or obese.
Given that MSG makes food tastier to most people, and could thereby cause people to eat more, the findings seem unsurprising at first blush.
However, people who used MSG regularly were more likely to be overweight even when their calorie intake and level of physical activity was the same as people who didn't use MSG.
Most major brands of canned tuna contain added MSG, but you won't find MSG listed on the label. Instead, the makers use one of the many MSG-rich substances used to disguise its presence (see the sidebar “MSG's many masks”, below).
Vital Choice Albacore Tuna is a rare exception. From day one, we've banned added glutamate from our foods (see “No MSG in Our Tuna: The Story of One Vital Choice”).
MSG renders rodents obese
The fact that MSG induces weight gain in lab animals is very well known. In fact, a search of the U.S. government's biomedical database (PubMed) for the term “MSG obese rat” yields 89 (generally disturbing) results.
Numerous studies show that feeding rats MSG during pregnancy and infancy alters levels of various hormones, increases appetite and calorie intake, and induces metabolic changes associated with increased risk of diabetes and heart disease, including damaging liver inflammation (Fernandez-Tresguerres Hernández JA 2005).
As the authors of a recent animal study wrote, “MSG treatment of mice induces obesity and diabetes… we suggest that MSG should have its safety profile re-examined and be potentially withdrawn from the food chain” (Nakanishi Y et al. 2008).
U.S.-Chinese study links MSG to weight gain
Because MSG is used in many processed foods, finding groups of people with similar diets who do and don't consume MSG has been difficult.
Researchers at the University of North Carolina (UNC) worked with scientists from Chinese institutions, who recruited 752 middle-aged Chinese men and women in rural villages in northern and southern China (He K et al. 2008).
The people in these relatively remote areas use very little commercially processed food, most of which contains some form of added MSG.
This made it possible to identify people who used no MSG at all, amidst the eight in 10 residents who added it to home-cooked fresh foods.
This high rate of MSG use seems unsurprising because MSG is cheap but produces some of the flavor sensations associated with meat, which remains relatively scarce and costly in rural China.
Results put MSG in unhealthful light
The MSG users among the villagers were divided into three groups, based on the amount of MSG they used.
And the results of the investigation showed that the third of the villagers who used the most MSG were nearly three times more likely to be overweight, compared with non-users.
The study was led by UNC nutritional epidemiologist Ka He, M.D., MPH, who made an important point concerning the study's implications:
“The U.S. Food and Drug Administration and other health organizations around the world have concluded that MSG is safe, but the question remains—is it healthy?” (UNC 2008).
Why would glutamate produce health problems?
Glutamate is the principal “excitatory” neurotransmitter in the central nervous system, and serves as a signaling molecule in brain and other bodily cells.
It's critical to learning and memory formation, via formation of new networks among brain cells and regions of the brain: a process called “neuro-plasticity”. This may we why glutamate is the most abundant amino acid in human breast milk.
However, excessive accumulation of glutamate in the synapses between brain cells has been associated with a cell-damaging effect called “excitotoxicity” and excessive glutamate buildup is implicated in number of neurological disorders.
Damaging buildup of glutamate in synapses usually occurs because of a metabolic disorder, not because of dietary glutamate. Pure glutamate causes brain damage in infant rodents when it is administered in high doses, but not when they ingest glutamate in food.
(Interestingly, rats fed omega-3s display reversals in age-related deficits in the glutamate receptors of brain cells… see “New Insight into Anti-Aging Brain Benefits of Omega-3s.”)
But when researchers test MSG for safety they've looked for overt damage to cells and organs resulting from ingestion of MSG in foods.
They haven't looked in humans for the hormonal and appetite effects seen in rats, which could lead to metabolic changes and weight gain in people as well.
Hopefully, the results of the new U.S.-Chinese study will prompt health authorities to take a close look, and may, at minimum, lead to tougher labeling laws so that people know whether a packaged food contains added MSG or glutamate.
What is MSG?
The “active” flavor-enhancing ingredient in MSG is the amino acid (protein building block) called glutamate, which is found in all living organisms.
Glutamate has been used as food additive for enhancing flavor for about 1,200 years, because it imparts a unique, elusive taste known as “umami” in Japanese.
Umami is now recognized as the fifth basic taste, in addition to sweet, sour, bitter, and salty, and is usually described as savory, meaty, or brothy.
To be more specific, it is the form that glutamate adopts when broken down under heat – called l-glutamate – that produces the umami sensation.
Glutamate becomes l-glutamate when it breaks down in response to heat (e.g., cooking), fermentation (e.g., aged cheese or soy sauce) or ultraviolet sunrays (e.g., ripening tomatoes).
In late 1800's, restaurateur Auguste Escoffier became the most famous chef of all time—and the father of what we now think of as “French cuisine”—when he began serving meals that featured his unique veal stock.
Escoffier's enormous success rested almost entirely on the fact that his veal stock was rich in umami flavor.
Unbeknownst to him, Escoffier's veal stock imparted this fabulous, mysterious flavor because its method of creation produced large concentrations of l-glutamate.
Simultaneously, the Japanese chemist Kikunae Ikeda was trying to figure out why dashi—the classic Japanese seaweed soup commonly used as a stock—tasted so indefinably good.
Ikeda finally isolated l-glutamate as the mysterious element in dashi, and he named the taste umami, which translates as “delicious”.
Pure MSG was synthesized early in the 20th century, and has since become widely used in packaged and restaurant foods around the world.
Far be it from us to suggest that people forgo the delightful flavor of umami.
But manufacturers intent on appealing to consumers' inherent taste for umami seem to have gone much too far by adding l-glutamate to every food in sight… thereby making people fatter in the bargain.
- Diniz YS, Faine LA, Galhardi CM, Rodrigues HG, Ebaid GX, Burneiko RC, Cicogna AC, Novelli EL. Monosodium glutamate in standard and high-fiber diets: metabolic syndrome and oxidative stress in rats. Nutrition. 2005 Jun;21(6):749-55.
- Fernandez-Tresguerres Hernández JA. [Effect of monosodium glutamate given orally on appetite control (a new theory for the obesity epidemic)] An R Acad Nac Med (Madr). 2005;122(2):341-55; discussion 355-60. Spanish.
- He K, Zhao L, Daviglus ML, Dyer AR, Van Horn L, Garside D, Zhu L, Guo D, Wu Y, Zhou B, Stamler J; INTERMAP Cooperative Research Group. Association of monosodium glutamate intake with overweight in Chinese adults: the INTERMAP Study. Obesity (Silver Spring). 2008 Aug;16(8):1875-80. Epub 2008 May 22.
- Hermanussen M. Nutritional protein intake is associated with body mass index in young adolescents. Georgian Med News. 2008 Mar;(156):84-8.
- Krulwich R. Sweet, Sour, Salty, Bitter… and Umami. NPR Morning Edition, November 5, 2007. Accessed online September 5, 2008 at http://www.npr.org/templates/story/story.php?storyId=15819485
- Nakanishi Y, Tsuneyama K, Fujimoto M, Salunga TL, Nomoto K, An JL, Takano Y, Iizuka S, Nagata M, Suzuki W, Shimada T, Aburada M, Nakano M, Selmi C, Gershwin ME. Monosodium glutamate (MSG): a villain and promoter of liver inflammation and dysplasia. J Autoimmun. 2008 Feb-Mar;30(1-2):42-50.
- University of North Carolina at Chapel Hill (UNC). UNC researchers find MSG use linked to obesity. Wednesday, August 13, 2008. Accessed online September 2, 2008 at http://uncnews.unc.edu/news/health-and-medicine/unc-researchers-find-msg-use-linked-to-obesity.html