Thinking with your Stomach

May 31, 2013

By Medical Discovery News

“The way to a man’s heart is through his stomach.” New research might amend this common proverb to “the way to a man’s brain is through his stomach.” An article in the “New Scientist” argues that the enteric nervous system (ENS), found in the tissues of the gastrointestinal (GI) tract, functions as a second brain of sorts.

Spanning the mouth to anus, the GI system is approximately 30 feet long and can be divided into the upper (esophagus, stomach, and duodenum) and lower (large and small intestine) tracts. This is where digestion occurs, providing metabolic functions and energy to the body. With this complex role, it is not hard to imagine why it needs its own nervous system.

Like the brain, the ENS consists of different types of neurons as well as glial cells, which provide support and protection for the neurons. The human ENS contains upward of 500 million neurons and an equal number of glial cells, more than all of those in a rodent’s brain. However, the human brain contains 90 billion neurons. The ENS communicates with the brain to control unconscious or autonomic processes, like peristalsis, the wave-like motions that push food through the GI tract. 

To accomplish this, the ENS produces hormones and neurotransmitters much like the brain. In fact, the ENS produces as much dopamine (which triggers feelings of reward and pleasure) as the brain and most of the serotonin (which controls mood, appetite, and sleep) within the body.

So, if the ENS truly acts as a second brain, then the GI system can affect a person’s moods and sense of wellbeing. The ENS causes this by transmitting signals to the brain through the vagus nerve. This makes sense, since people typically feel good after enjoying a meal. For example, when rich foods are digested they release fatty acids. The gut detects this, prompting the ENS to send certain signals to the brain. According to brain imaging studies, the brain then releases pleasurable sensations, altering a person’s mood. So it’s no wonder that people crave rich, fatty foods!

On the other hand, people usually eat differently when stressed. Stress can lead to the production of a GI hormone called ghrelin, which causes feelings of hunger and leads to a reduction of anxiety and depression. In experiments, mice subjected to stress sought out fatty foods, which elevated the production of ghrelin. The link between chronic stress and obesity is then a no-brainer.

The main function of the ENS is to monitor the digestion of food and identify threats in what is eaten, such as toxins or infections. So, perhaps listening to the stomach when it comes to choosing meals isn’t all bad. After all, that’s the second brain at work.