If anything makes us human it’s our minds, thoughts and emotions. And yet a controversial new concept is emerging that claims gut bacteria are an invisible hand altering our brains. Science is piecing together how the trillions of microbes that live on and in all of us—our microbiome—affect our physical health. How could bacteria be altering the brain? The brain is the most complex object in the known universe so how could it be reacting to bacteria in the gut? One route is the vagus nerve, it’s an information superhighway connecting the brain and the gut.Bacteria break down fiber in the diet into chemicals called short-chain fatty acids, which can have effects throughout the body.The microbiome influences the immune system, which has also been implicated in brain disorders.There is even emerging evidence that gut bugs could be using tiny strips of genetic code called microRNAs to alter how DNA works in nerve cells.