A group of researchers at Spain's Faculty of Medicine at the Complutense University of Madrid have concluded that the addition of MSG (Monosodium glutamate) to foods made be responsible for obesity in adults and that MSG is especially detrimental for children.

The scientists conducted tests on laboratory rats feeding them small doses of the flavour enhancer and discovered that E-621 produced a massive 40% increase in appetite in the rats. The tests suggest the additive affects an area of the brain responsible for controlling appetite that prevents proper functioning of the body's appetite control mechanisms.

The more food people eat with MSG added to how hungry they feel, say the scientists, and the more they will eat. Food companies are obliged by law to list E-621 in the ingredients, but they do not have to specify the quantity used.