Monosodium glutamate is a self-limiting substance. Once the proper amount is used, additional use contributes little, if anything at all, to food flavor. In fact, adding too much monosodium glutamate can result in a decline in palatability.

Source: Yamaguchi, S and Takahashi, C., 1984; Agric. Biol. Chem. 48:1077-1081.