Your Digestive Tract and your Nervous System:
This week we are going to discuss the digestive tract, how it works with your microbiome, and your nervous system.
Starting at the beginning of your digestive tract your mouth provides accommodation to hundreds of species of bacteria, including a fairly rough crowd of Streptococcus and Staphylococcus, bacteria known to cause disease. In a healthy person these are generally not troublesome, being held in check by other bacteria. In a person with gut dysbiosis the bad bacteria are no longer in check causing sugar cravings, which will create short term bliss, but long term sugar centered microbiota can potentially make you anxious and depressed. Jumping back to your mouth, we have home-brewed antibiotics in there! This is a part of your innate immune system, and many pathogens are immediately killed right here in your mouth thanks to the copious flows of saliva. Another system in your body is called the enteric nervous system (ENS)—the gut’s nervous system, which is large and complex enough to be called the second brain. We’ll talk more about that in a bit. Did you know people with anxiety are three times more likely to have GERD, so from a psychobiotic point of view, this connection to mental health is important. Going back to your GI tract as food and the microbes that come with it travel down your esophagus they enter the stomach where most species die. Only a select group of microbes, including Candida, Helicobacter, and Lactobacillus species, can handle the acidity in your stomach. This points to a problem not just with psychobiotics, but also with probiotics in general: Each species can have quite different effects, and those effects may even change with their surroundings. When it comes to microbes, easy answers are elusive. From the time you start to eat solid food, you develop a core set of bacteria that may stay with you for life—or at least until you take antibiotics and kill them off. Even then, many microbes in your custom microbiota will usually return because they are able to hide deep in the crypts of your intestines. The standard American low-fiber diet, coupled with a steady drumbeat of antibiotic treatments, has come close to wiping out certain bacterial species in the Western world. It is possible that we are driving some microbial species to extinction. If some of these have psychobiotic properties, we could be affecting our collective mood without realizing it. The disappearance of beneficial microbes could, in fact, be a major contributor to the alarming rise in anxiety and depression seen around the world. But fiber is manna for the microbes living in your large intestine, and they squeeze out a surprising amount of useful fuel that can then be absorbed by your gut. Both Crohn’s and UC involve inflammation, which is often associated with anxiety and depression, highlighting a gut-brain connection. Moving down the GI tract to your colon. The extra size of your colon means that there is plenty of time and room for the chyme to slowly inch by, bubbling and fermenting as it goes. This is the source of flatulence, which is actually a sign of a properly functioning microbiota. Your colon pampers the bacteria that produce vitamins that humans cannot normally synthesize. Bifido, Lacto, and Propionibacteria can all produce B vitamins, including B12, thiamine, riboflavin, niacin, biotin, and folic acid. A shortage of these vitamins can lead to depression, so here is yet another major psychobiotic contribution made by these microbes in your large intestine. And that’s not all: Bacteria like E. coli help produce various forms of vitamin K, important in blood clotting. You can find it in green vegetables, but the bacteria in your gut make the bulk of what you use. Babies without a good bacterial system in place may not be able to get enough vitamin K, and it is common to give newborns a shot of it to get them started. There is also some evidence that vitamin K can reduce anxiety. The fact is: Your bacteria naturally produce neurotransmitters in a volume that rivals that provided by prescription drugs. For instance, Lacto and Bifido, two of the bacteria genera abundant in your colon, both produce GABA (gamma aminobutyric acid), a key neurotransmitter that can have a tranquilizing effect, dialing down your anxiety. In the colon, Streptococcus and Escherichia species produce serotonin—the “happiness” neurotransmitter that is an important player in mood and provides the guiding rationale for selective serotonin reuptake inhibitors (SSRIs), a class of drugs designed to maintain serotonin levels in the body and now the most popular type of drug prescribed for mood disorders. Some 90 percent of the body’s serotonin is found in the gut. That’s because your gut—the second brain —uses the same neuroactive chemicals to compute and process information as the first brain does. Accumulating data now indicate that the gut microbiota communicates with the central nervous system (CNS) through neural, immune, and endocrine pathways—and thereby influences brain function and behavior. There are three main communication channels between your brain and your gut: your nervous system, your immune system, and your endocrine system. The circulatory and lymphatic systems also play supporting roles, but these first three are dominant. The nervous system relays information to and throughout your brain. It communicates using chemicals called neurotransmitters. Its communication style is fast and point to point, but short-acting. The immune system is at the ready to rally a defensive response against threats to healthy homeostasis. It uses the protein molecules called cytokines to signal distress. It can communicate quickly, but its urgent chemical effect can be harsh enough to cause tissue damage. The endocrine system monitors and manages growth and metabolism. Its component glands communicate by secreting hormones into your blood and thus sending signals throughout the body. Its operations are slower, more moderate and systemic, but longer-acting than those of the other two systems. The nervous system has two major divisions: the central nervous system (CNS), composed of the brain and spine, and the peripheral nervous system, less well known but just as important. The peripheral nervous system divides into four parts: somatic, sympathetic, parasympathetic, and enteric. To achieve optimal gut-brain health, all four parts are operative, in balance, and in communication with one another and with the CNS. You use the somatic nervous system whenever you voluntarily do anything. In the context of psychobiotics, the somatic system matters because you maintain voluntary control over what you eat (or don’t eat)—and thus, you exert some nervous system control over your microbiota. The sympathetic nervous system is the part often nicknamed “fight or flight.” when it’s activated, in other words, all other systems get put on the back burner. The stresses that activate this system can be external—or internal—tension held in muscles or, pertinent to psychobiotics, food habits that trigger continued inflammation in the gut. The parasympathetic nervous system has a nickname, too: “feed and breed.” When the parasympathetic nervous system is chugging along, you achieve a state of health, happiness, and balance we all strive for. The enteric nervous system is the one that operates in your gut, your second brain. This system, including your microbiota, holds the keys to dismantling any chronic stress responses you may be experiencing, and to returning your body to a healthy homeostasis. All three of these systems operate on autopilot, so typically you don’t even think about them.
