What exactly is the connection between brain and gut? The brain sends signals to the digestive tract through the sympathetic nervous system and the parasympathetic system. The sending and receiving of these signals play a big role in how effectively your body absorbs nutrients, how fast your body digests foods and the level of inflammation in the digestive system.

Dr. Michael Gershon, Chairman of the Department of Anatomy and Cell Biology at New York–Presbyterian Hospital/Columbia University Medical Center, an expert in the nascent field of neurogastroenterology and author of the 1998 book The Second Brain, explains that the phrase “second brain” doesn’t really mean the bowel can solve mathematical problems or write poetry by itself. Rather, what it brings to life is the fact that the entire digestive tract works as a single entity. Connecting these parts is an incredibly complex network of nerve cells, supporting cells, proteins and chemical messengers, which send messages back and forth, much like those found in the brain. In fact, the bowel contains about the same amount of nerves as the brain, and far more than the spinal cord.

In addition to being in charge of the digestive process, your gut lining is the core of your body’s immune system and defends you against such foreign invaders as viruses and bacteria. “It’s a very important barrier, as important as the skin,” says Dr. Gershon.