Monosodium glutamate (MSG) is a popular food additive found in many commercially prepared and packaged foods. Numerous studies have linked it to obesity, brain damage, macular degeneration and liver damage, yet it is still found in many of the foods we eat.
MSG Is Linked to Obesity
Recent research has shown that monosodium glutamate (MSG) causes weight gain and obesity in lab animals, and that it can have the same effect in humans.
The research was reported in the journal obesity, and found that the food additive damaged the appetite regulation center in the hypothalamus (an area of the brain), causing leptin resistance. Leptin is a protein hormone that regulates energy intake and energy expenditure, including appetite and metabolism.
Researchers conducted a cross-sectional study in China, and participants were told to add quantified amounts of MSG when preparing their foods. After adjusting for confounders including physical activity and total energy intake, the researchers found that MSG consumption was positively related to increases in body mass index.
"Animal studies indicate that monosodium glutamate (MSG) can induce hypothalamic lesions and leptin resistance, possibly influencing energy balance, leading to overweight. This study examines the association between MSG intake and overweight in humans. ... With adjustment for potential confounders including physical activity and total energy intake, MSG intake was positively related to BMI. Prevalence of overweight was significantly higher in MSG users than nonusers.
This research provides data that MSG intake may be associated with increased risk of overweight independent of physical activity and total energy intake in humans."
He K et al 2008 Association of monosodium glutamate Intake With overweight in Chinese Adults: The INTERMAP Study obesity 16, 1875 - 1880
MSG Can Cause brain Damage
MSG is considered a neurotoxin, and many studies have linked this food additive to brain damage in animals. MSG is the sodium salt of glutamate, and glutamate is one of the more commonly known excitotoxins (another one is aspartame). Glutamate is a normal neurotransmitter in the brain, but only exists in the extracellular (outside the cell) fluid of the brain in very, very small concentrations. When the concentration of this transmitter rises, the neurons begin to fire abnormally, and the cells undergo this specialized process of delayed cell death, excitotoxicity. Studies have shown that these effects are subtle and develop over a long period of time, although some people have a greater sensitivity and can develop more severe symptoms of excitotoxicity. The many studies that provide the evidence for this are given below in the references.
MSG and Macular Degeneration
Studies show that MSG can cause macular degeneration (retinal degeneration). In a 2002 study, researchers found that when MSG was fed to laboratory animals for 3 months and 6 months, observable retinal damage was seen.
"The present study suggests that a diet with excess sodium glutamate over a period of several years may increase glutamate concentrations in vitreous and may cause retinal cell destruction."
Ohguro H et al A high dietary intake of sodium glutamate as flavoring (Ajinomoto) causes gross changes in retinal morphology and function. Experimental Eye Research 75:(3), 2002.
MSG Promotes Liver inflammation and Dysplasia
In a 2008 study reported in the Journal of Autoimmunity, researchers reported that injecting MSG in mice lead to significant liver inflammation along with obesity and type 2 diabetes. Researchers looked at the long-term consequences of MSG on inflammation, by analyzing MSG injected mice and focusing in particular on liver pathology.
They found that by the age of 6 and 12 months, all MSG treated mice developed liver inflammation and structural abnormal change (dysplasia), and lesions were detected in some cases.
"We submit that MSG treatment of mice induces obesity and diabetes with steatosis and steatohepatitis resembling human NAFLD and NASH with pre-neoplastic lesions. These results take on considerable significance in light of the widespread usage of dietary MSG and we suggest that MSG should have its safety profile re-examined and be potentially withdrawn from the food chain."
Nakanishi Y et al 2008 Monosodium glutamate (MSG): A villain and promoter of liver inflammation and dysplasia Journal of Autoimmunity Vol 30, 1-2, P 42-50
MSG is a Widely-used Flavor Enhancer
A lot of canned, processed and pre-packed food and fast food contains MSG, but it is frequently listed under various names on the food label. Some of the many names used are: hydrolyzed vegetable protein, autolyzed vegetable protein, textured vegetable protein, hydrolyzed yeast extract, autolyzed yeast extract, plant protein extract, sodium caseinate, calcium caseinate, yeast extract, textured whey protein, and textured soy protein. Even the terms spice and natural flavor can indicate the presence of MSG.
The best way avoid MSG is by buying whole foods and preparing them at home. The next best thing is to read the labels and know the various disguises under which MSG is known, and avoid these foods.
- Nakayama D et al 2003 Turnover of Acinar and Islet Cells in the Pancreas of Monosodium Glutamate-Treated obese Mice obesity Research 11, 87 94.
- Olney, J.W. Brain lesions, obesity, and other disturbances in mice treated with monosodium glutamate. Science 164: 719-721, 1969.
- Snapir, N., Robinzon, B., and Perek, M. Brain damage in the male domestic fowl treated with monosodium glutamate. Poult Sci 50: 1511-1514, 1971.
- Arees, E.A., and Mayer, J. Monosodium glutamate-induced brain lesions: electron microscopic examination. Science 170: 549-550, 1970.
- Arees, E.A., and Mayer, J. Monosodium glutamate-induced brain lesions in mice. Presented at the 47th Annual Meeting of American Association of Neuropathologists, Puerto Rico, June 25-27, 1971. J Neuropath Exp Neurol 31: 181, 1972.
- Everly, J.L. Light microscopy examination of monosodium glutamate induced lesions in the brain of fetal and neonatal rats. Anat Rec 169: 312, 1971.
- Olney, J.W. Sharpe, L.G., Feigin, R.D. Glutamate-induced brain damage in infant primates. J Neuropathol Exp Neurol 31: 464-488, 1972.
- Lemkey-Johnston, N., and Reynolds, W.A. Incidence and extent of brain lesions in mice following ingestion of monosodium glutamate (MSG). Anat Rec 172: 354, 1972.