Monosodium glutamate (MSG) is a food ingredient which is used to enhance flavour and palatability. It is the glutamate – an amino acid - part of the MSG molecule that does the job in this respect. MSG (and/or other sources of glutamate) can be found in a wide range of processed foods with the blessing of our Governments and food agencies. However, there has been lingering concern that glutamate might have some adverse affects on health, in a way which parallels the situation with the artificial sweetener aspartame.
One concern about aspartame has been that, despite being virtually devoid of calories, it might be contributing to the burden of overweight and obesity rather than helping here. It seems that in the case of aspartame, this substance has some capacity to stimulate appetite.
Some have leveled a charge that MSG may promote weight gain on the basis of experiments which show it has the potential for this unwanted side-effect in animals. However, until recently, the relationship between MSG consumption and weight had not been assessed in humans.
That changed on the publication of a study this month in the journal Obesity . The study, conducted in China, assessed the relationship between MSG consumption and body mass index (BMI) in 752 men and women aged 40-59. The researchers divided the participants in this study into three bands, according to MSG consumption. Compared to those in the lowest consumption band, those in the highest were found to be 2.75 times more likely to have a BMI of more than 25.
This link between MSG consumption and increased body weight may have many explanations. The two obvious ones are that MSG somehow led individuals to consume more food or be less active. However, in this study, the authors accounted for these potential factors, which means that the link between MSG consumption and increased body weight appears to be independent of these factors.
The suggestion here is that MSG/glutamate may have one or more metabolic effects in the body which might predispose consumers to weight gain. As it happens, administering MSG to animals has been shown to induce various changes that promote fat accumulation including suppression of fat breakdown (lipolysis) . The free full text version of this study is linked to below, which details other effects of MSG that might affect body weight in the long term.
What is required now is for more work to be done to assess what effects MSG might have on human physiology that might cause weight gain. Because, if one of the most commonly used food additives does indeed have the potential to cause weight gain, then it’s only right that we should know.
1. He K, et al. Association of Monosodium Glutamate Intake With Overweight in Chinese Adults: The INTERMAP Study. Obesity 2008;16(8):1875–1880