We have all felt it—the way strong emotions such as anxiety, stress, excitement, love, and grief can hit us right in the gut. Our language is full of descriptions: “butterflies in my stomach” when madly in love, the “sinking feeling” in our stomachs when things start to go wrong, bad news experienced as a “kick in the gut,” the “knot in my stomach” when very anxious, witnessing something disturbing that “makes me sick to my stomach,” and anger that sends our “stomachs churning.” We see the movie scenes of people doubled over vomiting after hearing sudden bad news. And it’s well known that stress affects our digestive system in unpleasant ways. Anxiety also worsens pre-existing gastrointestinal conditions such as irritable bowel syndrome (IBS).
More recently, we are learning that the connection between our emotions and our gut is much more complicated and is bi-directional. What goes on in our digestive system affects our brain in complex ways not yet fully understood. The gut contains a nervous system of its own, the “enteric nervous system” (ENS), which facilitates digestion. It is now understood that the ENS communicates with our central nervous system (CNS), sending signals to the brain through various pathways. (The ENS is sometimes referred to as “the second brain.”)
The mechanisms underlying this two-way communication include: signaling along the vagus nerve; proteins and hormones released by the ENS into the bloodstream, which then travel to the brain; immune system modulation; and our microbiome (see below).
The vagus nerve is involved in regulation of internal systems such as heart rate and digestion. The cells and microorganisms of the gut release a wide variety of hormones and peptides, which can then stimulate the vagus nerve. The vagus transmits the information to the brain, thus playing an important role in the regulation of processes such as energy balance, release of stress hormones, and sensations of hunger vs. satiety.
Our microbiome consists of trillions of microorganisms (including bacteria, viruses and fungi) which co-exist with us in our gut and perform many important functions. For example, these microorganisms produce chemicals our bodies need to function, such as amino acids, vitamins, and neurotransmitters. The vast majority of the body’s serotonin is produced by gut bacteria. These microorganisms also help digest certain foods such as those rich in fiber and can protect us against toxins and pathogens we may ingest. They also protect the lining of our intestines, forming a barrier to prevent the “leaking” of toxins, food and harmful organisms from the gut into the surrounding tissues.
The health and diversity of our microbiome seems to play a role in our mental wellness. An unbalanced or sparse microbiome has been linked with depression and anxiety. One of several ways a healthy microbiome helps protect against depression appears to involve its important role in modulating inflammatory pathways and in mediating the stress response. There is growing evidence that chronic inflammation and chronic stress contribute to mental disorders such as depression. (This is also the case with other illnesses such as cancer, heart disease, diabetes, obesity and many others.)
Some studies show decreased rates of depression and anxiety, as well as improved sleep, with the use of probiotics. Researchers are also looking into the role the microbiome might play in disorders such as schizophrenia, autism, OCD and addiction.
Given what we are learning, it seems important for our mental and physical health to foster a healthy microbiome.
Our microbiome is partially established during passage through the birth canal, so there is some concern about the rise in C-section rates. Diet is the other main contributor to building a diverse and healthy microbiome (see below). Aerobic exercise also has a positive effect. On the other hand, antibiotics have a negative impact by killing off beneficial gut bacteria. Physicians are paying more attention to reducing over-use of antibiotics for this reason (and also because it is a main culprit in the rise in antibiotic-resistant bacteria.) Another factor is our growing tendency to live in an overly sterile environment: too much hand sanitizer and sealed-off indoor environments, too little playing in the dirt.
In terms of diet, “prebiotics” are foods containing certain fibers which provide nutrition to support the growth of gut microflora. These include onions, garlic, leeks, asparagus, bananas, chicory root, and celery. There is some evidence that prebiotics are associated with lower morning cortisol levels (a stress hormone).
“Probiotics” are the actual bacteria, which can come in the form of foods (and drinks) or capsules. These foods include yogurt, sauerkraut, kombucha, sourdough bread, aged cheeses, Kimchi, kefir and miso. In general, a diet rich in fruits and vegetables, fish, whole grains, and fermented foods is most beneficial. I’m glad to say that coffee and dark chocolate, walnuts and turmeric are on the list of helpful foods. Fried, processed, sugary and fast foods have a negative effect. It’s also best to limit red meat intake. This type of diet also has many other benefits, including heart health and brain health.
Probiotic capsules are marketed as containing active bacteria (avoid taking these if you are immunocompromised). Eating a microbiome-friendly diet is the best approach, with no need to then add capsules, but capsules can be considered. One problem is that many do not actually contain what they claim to and therefore may be a waste of money. You can look for products approved by ConsumerLabs or US Pharmacopeia to find higher quality brands.
Next time you make your grocery list, think about feeding your brain!