The human digestive tract is home to trillions of microorganisms, including bacteria, viruses, fungi, and parasites, that are collectively referred to as the gut microbiota. These microbes add an extraordinary 9 million genes to our bodies; for reference, the human genome contains a mere 23,000 genes! (1) Essentially, this makes us more microbial than human! Caring for our gut microbes is, therefore, a prerequisite for good health.
In previous blog posts, I have discussed at length the impact of dietary factors on the gut microbiota. In this blog, I’d like to switch gears and discuss a non-nutritive factor that profoundly impacts our gut microbes – chronic stress.
Stress and your gut microbes
Stress is defined as a physical, mental, or emotional factor that causes bodily or mental tension. In our hard-charging society, stress is a ubiquitous part of daily life. Small doses of stress can be beneficial – strengthening neuronal connections in the brain, increasing mental and emotional resilience, and driving us to succeed. However, when stress becomes chronic, it can have serious adverse effects on our health and well being.
For years, scientists have understood that the human gut microbiota influences the body’s stress response by altering neurotransmitter and hormone signaling. More recently, it has become apparent that this link is a two-way street – chronic activation of the stress response system also impacts our gut microbes. Different types of stress, including psychological, circadian, and environmental stress, have different adverse effects on the gut microbiota.
Work and finance-related anxiety, loneliness, and unhealthy relationships are familiar sources of psychological stress in our modern-day world. A growing body of research indicates that psychological stress alters the gut microbiota. Animal models of mental stress (the social defeat, restraint, and water-avoidance models) which induce anxiety- and PTSD-like behaviors, reduce beneficial gut bacterial species and overall microbial diversity. (2) Higher gut microbial diversity is associated with optimal health, whereas reduced diversity is related to a variety of chronic health problems.
Chronic unpredictable mild stress significantly depletes Lactobacillus, one of the primary genera of beneficial bacteria in the gut. In fact, a fascinating observational study found that fecal lactic acid bacteria (which include Lactobacillus) were significantly reduced in undergraduate students during exam week. (3) If changes this dramatic can occur in a week, imagine what can happen to your gut microbes after months or years of chronic stress! Conversely, supplementation with Lactobacillus probiotics alleviates stress-induced anxiety-like and depressive behaviors in animals. (4)
While the mechanisms by which chronic stress impact the gut microbiota are not completely understood, we do know that catecholamines (such as epinephrine and norepinephrine) and other stress hormones directly affect the growth of pathogenic microbes like E. coli. (5) Stress-induced neurotransmitter signaling also reduces gastric acid production and intestinal motility, allowing the overgrowth of microbes in the small intestine.
Circadian disruption is a common source of chronic stress that is induced by factors such as abnormal sleep/wake schedules and excessive blue light exposure at night. Circadian disruption increases intestinal permeability (aka "leaky gut") and induces intestinal inflammation, creating an inhospitable environment for your commensal gut microbes. (5, 6) Circadian disruption may lead to increased levels of pro-inflammatory gut microbes and reduced microbial diversity. (7, 8)
Environmental stressors come in many forms, including chronic infections and toxic exposures (such as heavy metals, industrial pollutants, and mold). Cadmium and lead reduce beneficial butyrate-producing gut bacteria; butyrate is a natural compound with potent anti-inflammatory properties that shapes gut microbiota composition. (9) Mycotoxins, produced by harmful molds, deplete beneficial gut bacteria and enhance the growth of pathogens such as Shiga toxin-producing E. coli. (10)While there is not yet research on this topic, I suspect that the environmental stress posed by chronic Lyme disease may also alter the gut microbiota.
Reduce Stress to Heal Your Gut
If you are doing everything “right” in terms of diet and lifestyle but are still experiencing gut dysbiosis, SIBO, candida overgrowth, or other chronic health issues, it may be time to consider whether chronic stress is harming your gut microbiota and preventing you from healing.
Endeavoring to reduce chronic stress in our lives is not easy. It requires that we ask critical questions of ourselves, such as "Is this high-stress career path really what's best for my body in the long-term?" or "Is this relationship with [insert name] helping or hurting my health?" It also requires that we find balance in our lives, letting go of some activities or obligations to make more room for self-care. In the long-run, making decisions that reduce your overall stress will serve you, and your gut microbes, well.
In addition to making broad changes that reduce chronic stress, I also recommend maintaining a daily stress-reduction practice that includes meditation or mindfulness exercises. I’m a big fan of the Waking Up app, a meditation app that offers convenient, short meditations that have a significant impact. Headspace and Calm are two more options great for meditation newbies. I personally fit in a meditation session every evening before bed, because I find the exercise quite helpful for inducing relaxation and sleep.
In addition to maintaining a consistent meditation practice, you should also work on correcting circadian disruption and environmental stress. Wearing blue-light-blocking glasses at night reduces your exposure to circadian rhythm-disrupting blue light and can help normalize your body’s stress response. Treating chronic infections and removing yourself from toxic exposures will also reduce your body’s overall stress load and give your gut microbiota the opportunity to recover.