From the book Excitotoxins – The Taste that Kills by Russell Blaylock

In experimental animals “MSG babies” are found to be short in stature, obese, and to have difficulty reproducing. This effect only becomes evident long after initial MSG exposure. More detailed studies have found that “MSG babies” have severe disorders involving several hormones normally produced by the hypothalamus.

Unfortunately, MSG is not the only taste enhancing food additive known to cause damage to the nervous system. In fact, there is a whole class of chemicals that can produce very similar damage – they all share one important property. When neutrons are exposed to these substances, they become very excited and fire their impulses very rapidly until they reach a state of extreme exhaustion. Several hours later these neutrons suddenly die, as if the cells were excited to death. As a result, neuroscientists have dubbed this class of chemicals “excitotoxins”.

Several of these “excitotoxins” are man made and are used as research tools.  Others are found in nature, such as glutamate, aspartate, and cysteine – all of which are amino acids. MSG is a modified form of glutamate acid in which sodium is added to the molecule. But the toxic portion is the glutamate acid, not the sodium. Often food manufacturers will mix MSG with other substances to disguise it, or use substances known to contain high concentrations of glutamate and/or aspartate. For example, the label designation “natural flavouring” may contain anywhere from 20 – 60 percent MSG.”