What we have learned over the past several decades is that the microorganisms within the colon (which include bacteria, fungi, and certain viruses — called collectively microbiota) play a major role in virtually every aspect of physiology and ongoing development.

Other functions these organisms perform within the human body include:

• Reducing inflammation

• Inhibiting cancer

• Maintaining immune health

• Producing important nutrients

• Playing a role in the manufacture of bile

• Secreting a number of neurotransmitters

• Playing a major role in stress adaptation

• Playing a crucial role in brain health and development

The human gut contains trillions of microorganisms — more than 100 times the number of genes as are found in our cells. In fact, there are thousands of different bacterial species within the colon alone.

Recent studies have shown that these microbiota are part of a complex network called the microbiota-gut brain axis, which also involves the nerves in the walls of the gastrointestinal tract, the autonomic nervous system (sympathetic and parasympathetic systems), the neuroendocrine system (special hormones), and the immune system. Basically, this axis amounts to a two-way communication link between the brain and the intestines.

The gut bacteria (microbiota) talk to the brain by special chemical messages, and the brain talks back to the gut via the vagus nerve and spinal nerves. There is compelling evidence that the development of the brain is dependent on a healthy assortment of gut microorganisms that colonize a baby’s intestines very soon after birth.

The main sources of these highly beneficial bacteria are in the mother’s birth canal during natural childbirth and by ingesting mother’s milk during breastfeeding.

Babies born by C-section and those that are bottle-fed have a different assortment of gut microbiota. This can affect their development and future health, especially behavioral health.