Monosodium glutamate, a flavor enhancing food additive, is the sodium salt of glutamic acid. It is used in foods such as concentrated soups, sauces, chips, meat products, puddings, seasonings and many processed foods. Better known as MSG, it is widely used in Asian cuisine. MSG is consumed daily in the rural area of Thailand and is a common additive in Thai cuisine with an average intake of 4g per day.

Earlier studies have showed that there is a relation between consumption of MSG and being overweight, and that those who consume MSG at an average of 0.33g per day in the diet are significantly more overweight than persons who don't use the substance, irrespective of physical activity and energy intake. Similarly, animal studies have also shown that elevated MSG intake leads to increased serum triglyceride, fasting glucose, and insulin levels, all of which are metabolic disorder bio-markers.

So, Tonkla Insawang from Department of Biochemistry, Faculty of Medicine, Khon Kaen University, Thailand, and colleagues conducted a study in rural Thai adults to determine whether MSG is associated with metabolic syndrome, irrespective of physical activity and calorie intake.

The study was completed in 349 adults aged 35 to 55 years from 324 families. The families were provided 250 g of MSG to be used as the sole source of MSG in meal preparation for 10 days.  The total consumption at the end of 10 days was recorded and the daily consumption of MSG per person was calculated. These adults were then evaluated for energy and nutrient intake, physical activity, and tobacco smoking. The incidence of being overweight, obesity, insulin resistance and metabolic syndrome were also evaluated.

The results showed that prevalence of metabolic syndrome was higher in the group that consumed the highest amount of daily MSG. They also found that risk of metabolic syndrome increased with every 1g increase in MSG intake, irrespective of physical activity level and calorie intake.

Although the investigators found a significant trend for increasing insulin levels and prevalence of insulin resistance with high MSG intake, the fasting blood sugar did not differ. This implies that MSG can raise insulin levels without altering glucose concentration and glucose tolerance.

Interestingly, despite there being significant relationship between insulin resistance, being overweight, and metabolic syndrome with MSG intake, the researchers found that  MSG consumption does not significantly increase risk of insulin resistance after adjusting for the factors such as age, gender, family history of diabetes, smoking status, physical activity, and daily energy intake. Therefore, the metabolic syndrome associated with MSG intake, they hypothesized, 'may not be due to the energy-intake-induced obesity leading to insulin resistance' but rather, the MSG may push the dietary glucose towards fat synthesis and activate the enzymes involved in fat biosynthesis and storage of fat in adipose tissue.

The researchers thus concluded that 'Higher amounts of individual MSG consumption are associated with the risk of having the metabolic syndrome and being overweight independent of other major determinants'.

Reference: Insawang, Tonkla, et. al. Monosodium glutamate (MSG) intake is associated with the prevalence of metabolic syndrome in a rural Thai population. Nutrition & Metabolism 2012.

Source-Medindia