Summary of David Perlmutter & Kristin Loberg's Brain Maker details the complex microbiome that lives in the human gut and how it affects the brain. Rising rates of Alzheimer’s disease, mood disorders, Attention Deficit Hyperactive Disorder (ADHD), multiple sclerosis, autism, and other conditions are linked to imbalances in the thousands of microorganisms that colonize the gut, primarily bacteria. Disruptions to this microbiome can begin at birth for children born via cesarean section because these babies do not acquire their mother’s microbiome traits from the birth canal. Instead, they pick up less beneficial bacteria from exposure to skin. Then there is the ultra-clean, antibiotic-laden, high stress lifestyle and low-fiber diet of the United States and other wealthy nations. Finally, exposure to environmental toxins also leads to disruptions to the microbiome.