A close reading of a list of classic McDonald's recipes from the '50s through the '70s reveals a disturbing amount of Monosodium Glutamate (MSG), a chemical whose potential health effects have caused considerable controversy.
However, the use of MSG in McDonald's food is not solely a matter of history. MSG is still present in some forms in many modern McDonald's products, including their Grilled Chicken Filet, Sausage Patty, and French Fries.
Many other foods on their menu, especially those that contain "natural flavors" or "hydrolyzed protein" as ingredients, also contain MSG. Most of the MSG is in the form of glutamic acid, the chemical's active component.
Studies have indicated that MSG can cause severe allergies and even brain damage. Most baby food companies have voluntarily stopped using MSG in their products.