Fat, Stressed, and Sick makes the case that processed food compromises health not just because of added sugar, salt, and fat, but also because these foods contain significant amounts of glutamate—aka MSG. MSG makes food deliciously addicting. What was not well-known until described here is that most of the MSG in processed food is created during food manufacturing. As the authors show, food processing of protein alone adds ten grams or more a day of MSG to the average American diet.

The book details the research linking dietary glutamate to a suite of inflammatory diseases: obesity, diabetes, autism, addiction, depression, and cancer, to name a few. Understanding the role of MSG in disease became the quest of author and biochemist Katherine Reid when she learned that her daughter's autism symptoms were associated with inflammation of the brain. Reid made the connection between inflammation and glutamate in the diet—a connection amply supported by other studies. In what became an experiment in her home, Reid examined every ingredient on every food label, removing all items with MSG and replacing them with whole foods. The results were swift and undeniable. Reid's discovery that what one ate mattered was the start of a program of food-based solutions to chronic inflammatory illnesses, through which now, a decade later, she has helped thousands of people.