There’s a reason we talk about “gut feelings” or knowing something “in our gut.” Our gastrointestinal system contains the enteric nervous system (ENS), a vast system of neurons often referred to as the second brain. The ENS is primarily concerned with controlling digestion, but its full range of function is much more complicated than just breaking down food, and is revolutionizing science’s understanding of the relationship between digestion, mood, and overall health.

The enteric nervous system

The nervous system consists of two parts: the central nervous system (CNS), which is made up of the brain and spinal cord, and the peripheral nervous system (PNS), which consists of the nerves and ganglia outside the brain and spinal cord. The PNS connects the brain and spinal cord to the limbs and organs. The enteric nervous system is part of the peripheral nervous system. The ENS helps move food through the gastrointestinal tract, releases enzymes to break food down, and directs the absorption of nutrients and elimination of waste.

The enteric nervous system is the largest and most complex part of the PNS, and contains between 200 and 600 million neurons — far more than the 100 million neurons in the spinal cord. The ENS is capable of autonomous function, and operates independently of the brain and spinal cord. It’s called the second brain for several reasons: it can control behaviors in the gut independently of the brain, although they are in constant communication. The ENS also makes use of more than 30 different neurotransmitters, including dopamine and serotonin, which are both related to mood. In fact, about 90 percent of the body’s serotonin is in the gut, as well as about 50 percent of its dopamine.

Although its primary role is controlling digestion, the role of the ENS goes far beyond processing food. Ninety percent of the fibers in the vagus nerve carry information from the gut to the brain, and not the other way around. This means the health and function of our gut have a significant impact on our mood and mental health. A large part of our emotions are likely influenced by our gut, and everyday emotional well being may rely on messages from the ENS. A healthy gut environment is therefore an important factor in good mental health.

The importance of proper digestion

Researchers are discovering evidence that irritation in the gastrointestinal system may send signals to the central nervous system that trigger mood changes. The ENS may trigger emotional changes in people with irritable bowel syndrome or other digestive problems such as constipation, bloating, and diarrhea. “For decades, researchers and doctors thought that anxiety and depression contributed to these problems. But our studies and others show that it may also be the other way around,” explains Jay Pasricha, M.D., director of the Johns Hopkins Center for Neurogastroenterology. “These new findings may explain why a higher-than-normal percentage of people with IBS and functional bowel problems develop depression and anxiety. That’s important, because up to 30 to 40 percent of the population has functional bowel problems at some point.”

The CNS and the ENS are in constant communication, so therapies intended for one may impact the other. For example, antidepressants are sometimes prescribed for irritable bowel syndrome since IBS may be related to an imbalance of serotonin.

Achieving good digestive health

To support both good digestive health and mental health, make sure you are eating a healthy diet that doesn’t put too much strain on your digestive system. Follow these tips to promote good digestive health.

  • Eat plenty of leafy greens and vegetables to help keep things moving and prevent constipation. Ideally, include some form of plant compounds in every meal.
  • Watch out for foods that can cause gastrointestinal irritation. Wheat, eggs, and dairy are common sources.
  • Drink plenty of water.
  • Get adequate levels of important electrolytes, such as potassium and magnesium.
  • Try eating less, snacking less between meals, and leaving more time between meals in order to reduce the burden on the digestive system. Prolonged fasting has been shown to alleviate digestive symptoms such as abdominal pain, abdominal distention, diarrhea, and nausea. You may also consider following a reduced-calorie fasting mimicking diet, which provides many of the same benefits of fasting while still allowing you to eat.