A small amount of MSG is sufficient to achieve optimum flavor.
The taste of MSG, like the taste of salt, is pleasant only within a relatively narrow concentration range. Further addition of MSG has little or no beneficial effect.
The amount of MSG used in foods is usually within the range of 0.1% and 0.8 % of the food as it is served. This is similar to levels of naturally occurring glutamate found in traditional dishes. The taste of monosodium glutamate (MSG) is self-limiting. This means that once the appropriate amount of MSG has been included in a recipe, adding more contributes little, if anything at all, to food flavor. In fact, adding too much MSG can result in a worse taste.
Here are two graphs that show the optimum level of MSG in a clear soup is 0.3% and the optimum level with fried rice is 0.37%:
MSG, like salt, is self-limiting. Here are two graphs which show similar results for salt in clear soup and in scrambled eggs: