Have you ever felt so nervous that you felt sick in the stomach, or had to go to the toilet? Research in the human gut microbiome is very new, but from the evidence, we now know about a process called the “gut-brain axis” . This is like a working relationship between the intestine and the brain. In fact, the gut is sometimes called the “second brain” because it has such a rich supply of nerves that control it and trigger pain signals. The products made by the gut bacteria, like GABA and butyric acid, act like neurotransmitters in the brain , which control moods and behavior. For example, we often notice changes in children’s behavior after they eat certain foods. And vice versa, when kids get anxious or irritated, their bowel movements sometimes change. Another example is how the infants with colic can have uncomfortable or irregular bowel motion.