MSG side effects include weight gain and brain damage. The nasty thing about this food additive is that it disrupts the leptin signaling pathway, which regulates fat metabolism. It is tricky to know where MSG is in your diet. Here is what you should know about what it does and how to avoid it.
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Image source: MSG: Hidden Sources

MSG Side Effects Research on Weight Gain

Scientists are finally starting to study how MSG causes weight gain. Here are some of the more recent references in the medical literature, with full abstracts. The highlighted text points out the main point of each article.

1. Am J Clin Nutr. 2011 Jun;93(6):1328-36. Epub 2011 Apr 6.

Consumption of monosodium glutamate in relation to incidence of overweight in Chinese adults: China Health and Nutrition Survey (CHNS).

He K, Du S, Xun P, Sharma S, Wang H, Zhai F, Popkin B.

Departments of Nutrition and Epidemiology, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. kahe@unc.edu

BACKGROUND: It has been hypothesized that monosodium glutamate (MSG), a flavor enhancer, is positively associated with weight gain, which influences energy balance through the disruption of the hypothalamic signaling cascade of leptin action.
OBJECTIVE: The objective was to examine the longitudinal association between MSG consumption and incidence of overweight.
DESIGN: Data were collected from the China Health and Nutrition Survey (CHNS), a prospective open-cohort, ongoing nationwide health and nutrition survey, consisting of 10,095 apparently healthy Chinese adults aged 18-65 y at entry from1991 to 2006. Diet, including MSG and other condiments, was assessed with a weighed food inventory in combination with three 24-h recalls. Incident overweight was defined as a body mass index (BMI; in kg/m(2)) ? 25 or ?23 based on World Health Organization recommendations for Asian populations. Multilevel mixed-effects models were constructed to estimate change in BMI, and Cox regression models with gamma shared frailty were used to determine the incidence of overweight.
RESULTS: The mean follow-up was 5.5 y. The cumulative mean (±SD) MSG intake of 2.2 ± 1.6 g/d was positively associated with BMI after adjustment for potential confounders and cluster effects at different levels (individual, household, and community). The adjusted hazard ratio of overweight was 1.33 (95% CI: 1.01, 1.75; P for trend < 0.01) for participants in the highest quintile of MSG intake compared with those in the lowest quintile after adjustment for age, physical activity, total energy intake, and other major lifestyle factors. CONCLUSIONS: MSG consumption was positively, longitudinally associated with overweight development among apparently healthy Chinese adults. Additional studies are needed to elucidate mechanisms of action and to establish causal inference.

2. Obesity (Silver Spring). 2008 Aug;16(8):1875-80. Epub 2008 May 22.

Association of monosodium glutamate intake with overweight in Chinese adults: the INTERMAP Study.

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.

Department of Nutrition, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.

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. We conducted a cross-sectional study involving 752 healthy Chinese (48.7% women), aged 40-59 years, randomly sampled from three rural villages in north and south China. The great majority of participants prepared their foods at home, without use of commercially processed foods. Diet was assessed with four in-depth multipass 24-h recalls. Participants were asked to demonstrate MSG amounts added in food preparation. Amounts shaken out were weighed by trained interviewers. Overweight was defined as BMI > or =25.0 or > or =23.0 kg/m(2)(based on World Health Organization recommendations for Asian populations). Eighty-two percent of participants were MSG users. Average intake was 0.33 g/day (s.d. = 0.40). 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. For users in the highest tertile of MSG intake compared to nonusers, the multivariable-adjusted odds ratios of overweight (BMI > or =23.0 and > or =25.0) were 2.10 (95% confidence interval, 1.13-3.90, P for trend across four MSG categories = 0.03) and 2.75 (95% confidence interval, 1.28-5.95, P = 0.04). 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.

MSG Side Effects Research on Brain Damage

3. J Pediatr Endocrinol Metab. 2003 Sep;16(7):965-8.

Does high glutamate intake cause obesity?

Hermanussen M, Tresguerres JA.

Aschauhof, Altenhof, Germany. hermanussen.aschauhof@t-online.de

World-wide obesity has risen to alarming levels. The average weight of German conscripts now increases by almost 400 g/year. Similar data were obtained in Austria, Norway and the UK. The rising prevalence of obesity coincides with a rising popularity of protein-rich diets. On average, Germans consume meat at 100 kg/year. Children eat some threefold more protein than recommended; infants of 6 to 12 months receive daily up to 5 g/kg body weight of protein. We hypothesise that it is not the protein, but the amino acid glutamate that determines the propensity of obesity. Chronic hyperglutamataemia may intoxicate arcuate nucleus (AN) neurons, thereby disrupting the hypothalamic signalling cascade of leptin action, causing hyperphagia, obesity and hyperleptinaemia. Hyperleptinaemia also exerts sympathetic effects including blood pressure elevation that are mediated via mechanisms different from the hypothalamic system, and other symptoms of the ‘metabolic syndrome’. This may happen even before birth when in small-for-gestational-age foetuses with impaired umbilical plasma flow, foetal hyperglutamataemia induces AN damage followed by later impairment of feeding regulation, hyperleptinaemia and symptoms that characterise the ‘thrifty phenotype’. We suggest abandoning the flavouring agent monosodium glutamate and reconsidering the recommended daily allowances of protein and amino acids, particularly during pregnancy.

Laboratory scientists use MSG as a research tool. In the article below, researchers wanted to know how leptin might be involved with certain brain receptors in the hypothalamus. They damaged these brain receptors experimentally with MSG, then followed the response of leptin (aka, the ‘master fat hormone’).

4. Am J Physiol. 1997 Jul;273(1 Pt 1):E202-6.

Attenuation of leptin-mediated effects by monosodium glutamate-induced arcuate nucleus damage.

Dawson R, Pelleymounter MA, Millard WJ, Liu S, Eppler B. Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville 32610, USA.

Leptin is a protein secreted by adipocytes that is important in regulating appetite and adiposity. Recent studies have suggested the presence of leptin receptors in the arcuate nucleus of the hypothalamus (ANH). Neonatal administration of monosodium glutamate (MSG) damages the ANH, resulting in obesity and neuroendocrine dysfunction. Neonatal administration of MSG was utilized to test the hypothesis that the anatomic site for many of leptin’s actions is the ANH. Female control (n = 6) and MSG-treated rats (n = 7) were implanted for 14 days with osmotic minipumps containing phosphate-buffered saline or leptin (1 mg.kg-1.day-1). Leptin suppressed (P < 0.05) body weight gain in controls but did not suppress weight gain in MSG-treated rats. Leptin decreased (P < 0.05) fat depots in controls but had no effect in MSG-treated rats. Night feeding was suppressed (P < 0.05) in leptin-treated control rats. MSG-treated rats showed a suppression in food intake that was of a smaller magnitude and appeared later in the course of leptin treatment. These findings suggest that leptin mediates some physiological actions related to fat mobilization via receptors located in the ANH.

Where Do You Get MSG in Your Diet?

This is very tricky, since there are so many ways that food manufacturers can include MSG in their products without having to list it directly on the label. Here is one of the best sources of information on this topic that I have found:

MSG – Hidden Sources

Weight gain is just one of the known MSG side effects. It is worthwhile to be careful to avoid this additive whenever you can.

Updating MSG side effects,

Dr. D