Let food be thy medicine and medicine be thy food.
Like most of America, I watched the Super Bowl last month, and like most of America for me the commercials were half of the appeal. I was struck in particular by one commercial that told a sad and touching tale of a man who envied other people’s bowel movements. It seems even dogs had it better than him as he watched wistfully as a dog relieved itself on the sidewalk. This man had a newly marketed condition called opioid-induced constipation as a result of being on chronic narcotics for chronic pain. He looked very sad as he window shopped for prune smoothies while melancholy violins played in the background.
The ad correctly notes that opioids (narcotics) block pain signals but can also block activity in the bowel.
Of course the ad was sponsored by a company that markets an expensive drug to counteract this side effect of the prescription narcotic abuse epidemic sweeping this country. No mention was made of the obvious solution of decreasing this poor man’s dependence on opioids.
Initially I was annoyed to see this approach to such a serious public health problem, but it got me thinking about the remarkable connection between the brain and the bowels. Why do opioids affect both the brain’s pain receptors and the intestine’s motility receptors? Because, as it turns out, we have a “second brain” in our intestines with the same receptors. Really.
When I was in medical school we were taught that the human nervous system was divided into two major components, the central nervous system and the peripheral nervous system. The central nervous system (CNS) is made up of the brain and spinal cord. The peripheral nervous system (PNS) encompasses the motor and sensory nerves and the autonomic nervous system, which is responsible for automatic functions like breathing and digestion. But there is a third separate nervous system, newly recognized, called the enteric nervous system that lives in the 27-foot-long human alimentary canal.
The enteric nervous system is comprised of more than 100 million nerve cells that operate mostly independently of the CNS and PNS. That’s more nerve cells than the spinal cord or the PNS have. More than 30 neurotransmitter chemicals are produced, with 95 percent of the body’s serotonin and 50 percent of the body’s dopamine produced in the enteric nervous system. Serotonin levels in the brain are closely associated with mood and are the major target of most antidepressant medications. Dopamine levels regulate pleasure centers in the brain. Serotonin levels in the gut seem to closely correlate with poorly understood disorders such as irritable bowel syndrome.
Why do we have an elaborate third nervous system in our guts? Because, like babies who put everything in their mouths, we interact much more with our environment internally than externally. The surface area of the GI tract is 100 times greater than the surface area of the skin. 100 trillion bacteria unseen by you live and produce molecules there. There is 100 times more bacterial DNA in a human than human DNA and 90 percent more bacterial cells than human cells. On average you are carrying around three pounds of bacteria in your gut although this fluctuates daily as 60 percent of the mass of each bowel movement is bacterial. No wonder that constipated guy is so unhappy. Too many pounds of bacteria.
The balance of the 500 to 1,000 species of bacteria that inhabit your colon primarily can vary quite a bit depending on the foods you eat and, of course, antibiotic use. Those bacteria are there for a reason, or reasons, and it seems unwise to unbalance them too much. They produce all sorts of chemicals that are used for blood clotting, protein building, immune function and neurotransmitters. This may be another reason constipated guy is unhappy, his serotonin and dopamine levels are unbalanced.
Like the previously mentioned babies, our understanding of this new field of neurogastroenterology is truly in its infancy, but it promises to revolutionize our approach to many medical and psychiatric disorders. We do know that the enteric brain does communicate with the brain directly through the vagus nerve and 90 percent of the communication is from the gut to the brain and not the other way around. Disorders such as depression may well be related to the function of our GI tract as much as our brains. Hippocrates was right all those years ago. You are what you eat.