Why do people become mentally ill? For years, researchers have debated possible causes, including genetics, chemical imbalances, stress, and social problems. Christopher M. Palmer, a Harvard psychiatrist, offers a new, unified theory of mental illness in Brain Energy (2022). Based on his research, Palmer asserts that mental illnesses stem from metabolic abnormalities of the brain, with contributing causes also including diet, exercise, environmental, and sleep issues. Patients need personalized treatment plans that account for all these factors, with better cross-specialty collaboration by medical professionals. More research is needed, too, which will require public support and funding. As understanding grows, new treatments will be found.