Monosodium glutamate (MSG) and the ribonucleotides disodium inosinate and disodium guanylate are commonly used as flavour enhancers in processed foods. The use of MSG is extensive, and annual world production of this compound exceeds 300 000 tons. MSG is a neurotoxin which effects the destruction of the arcuate nucleus (AR) of the hypothalamus when administered to mice.42,43 MSG is converted into the amino acid, glutamic acid, which is known to have neuroexcitory properties, and glutamate is also implicated in neurotransmission. Interest in MSG was stimulated after some people experienced symptoms such as tightening of the face and chest muscles and also a burning sensation in the upper body as well as headaches. This was called Chinese restaurant syndrome, because it was frequently experienced by patrons of Chinese restaurants and was traced to the liberal use of MSG by Chinese chefs.
Other symptoms associated with MSG are dizziness, diarrhoea, nausea and stomach cramps. Some children experience shudder attacks which may be mistaken for epilepsy, and long-term exposure in mice can lead to obesity.42,33 The most serious side effect of MSG is, however, its neurotoxic effect which also affects the endocrine function. MSG has been reported to depress growth hormone levels, and levels of prolactin and sex hormones are also affected.44,45,46 Such findings should make one extremely cautious of using MSG, and replacement products such as protein hydrolysates should also be avoided as they also contain large amounts of glutamate and thus have the potential to elicit similar effects.