Monosodium glutamate (MSG) has an E number of E621, and is used in the food industry as a flavour enhancer. It enhances the savoury flavour of foods, sometimes referred to as ‘umami’, and because of this it is used in a wide variety of foods to make them more palatable. Its use is widespread throughout the UK and America, meaning many people are potentially eating relatively large amounts. This article will investigate the health implications that consuming MSG can have on the body.
What is MSG?
Monosodium glutamate is simply a combination of a sodium ion and the amino acid glutamic acid. Both sodium and glutamic acid are abundant in our diet in the form of salt (which is sodium chloride) and proteins, which are made up of amino acids; glutamic acid being one of the most abundant. However, the glutamic acid in MSG is ‘free form’, whereas the glutamic acid in proteins is bonded to other amino acids. It is the abundance of free glutamic acid that MSG provides the body which causes concerns over its effect on our health.
MSG in the body
As MSG is a free from of glutamic acid, it doesn’t require any enzyme activity to break it down and can be rapidly absorbed by the cells in the intestine. The rate of absorption is only slowed by the presence of other foods which may physically prevent glutamic acid coming into contact with the cells. The cells in the intestine are specialised to be able to use glutamic acid as an energy source readily, and dietary glutamic acid makes up a significant proportion of the energy used by these cells1. Excess glutamic acid can also be converted into another amino acid called alanine in the intestinal cells. This means that consuming relatively small amounts of MSG (less than 3g)2 with food will not have any significant impact on glutamic acid levels in the blood, so unless you are sensitive to MSG, it should not have any impact on your health.
It is only when consumption of MSG exceeds 5g that free glutamic acid levels in the blood increase. In all healthy individuals, this amount of free glutamic acid can cause what is known as Chinese Restaurant Syndrome (CRS), the symptoms of which are very diverse, but can include skin rashes, depression, stomach cramps, migraines/ headaches, insomnia and irritable bowel syndrome (IBS) to name a few. Glutamic acid is involved in a number of biological mechanisms, which is why MSG can effect such a variety of biological functions. One function in particular is the role of glutamic acid as a neurotransmitter, and MSG has been linked to a number of serious mental disorders such as depression, anxiety, brain turmours and Alzhiemers disease3.
Effect of MSG on foetuses
MSG is known to cause lesions in the brain of human infants, the younger brains being more susceptible to damage. These lesions affect how chemical pathways are created, and can disrupt the development of the endocrine system. A study in young rats who were fed MSG as part of their diet showed that they were unable to escape from a maze and unable to discriminate between different stimuli.4 This shows that MSG had a very serious negative impact on the development of the rats brain, which may be the same in humans.
Glutamic acid has been shown to accumulate in mothers milk, and so breast feeding whilst eating foods high in MSG can cause the baby to consume dangerous levels of MSG. It is recommended to try and avoid foods high in MSG when pregnant or breast feeding, as it could potentially damage the brain of the foetus/ baby.3
Foods high in MSG
MSG is found in a variety of foods, but the quantity is often unknown because companies do not need to declare the amount on the labels, and there are a number of ways to disguise the free glutamic acid content of food. MSG is typically high in almost all highly processed food, and Chinese take-a-ways are notorious for containing high levels of MSG (resulting in over dosages of MSG being called Chinese Restaurant Syndrome). Looking on the label of foods, MSG is often labelled as one or more of the following:
- Flavour enhancers
- Hydrolyzed protein
- Stock/ broth
- Textured Protein
- Seasonings
- Natural pork/beef/chicken/ lamb flavours
- Corn starch
Any food label which contains the above in the ingredients is very likely to contain MSG, although with vague terms such as ‘seasoning’ (which could just mean salt and pepper) it is very difficult to be confident.
Summary
MSG provides the body with free form glutamic acid, an amino acid which is abundant in our diets. Our body is able to metabolise dosages of less than 3g per serving without having any ill effect on health, unless you are sensitive to glutamic acid. However, dosages of over 5g have been shown to significantly increase the amount of glutamic acid in the blood which can have very serious negative effects on health, particularly brain health. Research has shown that infant and foetus brains are very susceptible to the negative effects of MSG, and can cause lesions on the brain which seriously disrupt brain function.
References
1) Vernon R. Young et al. (2000). Glutamate: An Amino Acid of Particular Distinction. Journal of nutrition. 130 (4), 892S-900S
2) Kalapanda M.Appaiah. (2009). Monosodium Glutamate in Foods and its Biological Effects. In: Christine Boisrobert, Aleksandra Stjepanovic, Sangsuk Oh, Huub Lelieveld Ensuring Global Food Safety: Exploring Global Harmonization. n/a: Academic Press. 217-220.
3) Leber, M. J. (2008). Umami and MSG controversy: Cooks know the power of taste but are the ingredients safe? Food Market Place Review, 1–4
4) Munro, H. N. (1979) Factors in the regulation of glutamate metabolism. Filer, L. J., Jr Garattini, S. Kare, M. R. Reynolds, W. A. Wurtmaned, R. J. eds. Glutamic Acid: Advances in Biochemistry and Physiology :55-68 Raven Press New York. NY.
Image courtesy of su-lin.
