Like many people, I thought MSG — monosodium glutamate, a chemical compound used to enhance the flavor of food — was bad for me, and I was sure I felt terrible every time I ate it. After all, I was sluggish and had headaches and achy limbs whenever I ate a big meal in Chinatown. Now I know that the recurring headaches that plague me have little to do with what I eat. But at the time, avoiding those three letters brought me comfort and let me think I’d be eating some sort of sacredly pure meal made with food, not chemicals. Oh, how young and foolish I was....