New science on psychobiotics is helping us understand, and care for, our gut-brain connections.
What are Psychobiotics?
Psychoneuroimmunology is the study of how the mind influences health, and psychobiotics are bacteria that can provide mental health benefits by changing your gut microbiome. Originally, only certain bacteria and probiotics were thought to impact the mind and emotions. Now, research has shown that some prebiotics can also have psychobiotic effects. In fact, the field of psychobiotics is rapidly growing to include any influence on the brain that is carried out by bacteria.1
Psychobiotics can have emotional, behavioral, and cognitive effects as well as systemic benefits that support whole body health and wellbeing. The main pathways used by psychobiotics to elicit a gut-brain-body response are the enteric (digestive) nervous system, immune system, and vagus nerve.9,10
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Your Microbiome and the Gut-Brain Axis
The gut microbiome comprises all microorganisms that inhabit your intestinal tract. The gut-brain axis suggests that while your gut is affecting your brain, your brain is also affecting your gut, and the health of both are intertwined.1
We know, for example, that the gut microbiome is affected by mental health and stress. In one study, in the Journal of Pediatric Gastroenterology and Nutrition, infant monkeys whose mothers were startled by loud noises during pregnancy had fewer Lactobacilli and Bifidobacteria in their guts than those whose moms were not startled during gestation. Yet another study on mice by the same researchers, published in the journal Brain, Behavior, and Immunity, demonstrated that when a normal mouse shared a cage with a more “aggressive social disrupter” mouse, the good bacteria in the gut of the first mouse plummeted and the bad bacteria proliferated. This led to a series of health and immunity issues.
In another study, students had fewer Lactobacilli in their guts during a high-stress exam week than they did in the stress-free first week of school.9,10
One of the early studies on psychobiotics, in the Journal of Physiology, found that mice who were raised in sterile environments and maintained a sterile gut microbiome were uniquely ill-equipped to handle mental, emotional, and physical stress. When the mice were give a probiotic, there was a dramatic change in their stress-handling capacity, suggesting that a healthy diversity of gut bacteria can influence the brain. Higher stress hormone responses, including cortisol and adrenocorticotropic hormone (ACTH), as well as brain derived neurotrophic factor (BDNF), all dramatically improved with the probiotic. This was a pivotal example of probiotic-induced recolonization demonstrating a gut-brain effect, which is known as the hypothalamic–pituitary–adrenal (HPA) axis.2
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How the Gut-Brain Connection Works
The gut-brain connection is carried out by neurotransmitters that modulate mood, emotion, behavior, and the microbiome. A 2017 article published in the Handbook of Experimental Pharmacology found that 98% of the body’s serotonin was produced in the large intestine—now called the second brain.5
New research has mapped out which families of bacteria, or psychobiotics, are responsible for producing certain neurotransmitters in the gut. A diet high in indigestible fiber provides the fuel needed to support a healthy stable of gut psychobiotics. The Bacillus family of bacteria produces dopamine and noradrenalin, the Bifidobacteria family produces gamma aminobutyric acid (GABA), while the Lactobacilli family produces GABA and acetylcholine. The Enterococcus and Streptococcus families produce serotonin, and the Escherichia family produces noradrenalin and serotonin.
These families of bacteria also can modulate expressions of endocannabinoid receptors to produce psychotropic effects supporting a healthy and more stable mood.8
In a recent study, also in Brain, Behavior, and Immunity, 40 healthy male and female participants consumed either a placebo or a mixture of several probiotics, including strains of Bifidobacterium lactis and Lactobacillus acidophilus. Compared to the placebo group, the probiotic-treated group reported substantially less, sadness, reactivity to negative thoughts, rumination, and aggressive cognition, or anger.3
These results were supported a year later in a Trends in Neuroscience-published randomized double-blind study with 55 participants, mood and distress levels were self-reported. One group was given a probiotic consisting of Lactobacillus helveticus and Bifidobacterium longum while the other group received a placebo. Compared to the placebo, the probiotic group showed significant declines in self-reported negative mood and distress. The stress hormone cortisol was also lower in the probiotic group.1,4
Psychobiotics Protect a Leaky Gut
Stress raises cortisol and other stress hormone levels that have been shown to dysregulate the gut’s protective lining and reduce the integrity of the intestinal epithelium, or inner skin, creating a leaky gut that allows for the migration of bacteria from outside the gut microbiome. Gut-associated lymphatic tissue (GALT) responds to a leaky gut by triggering an immune and inflammation response that has been linked to mood-related concerns. Probiotic supplementation with the Bifidobacterium or Lactobacillus families has been shown to restore gut-barrier integrity and reduce stress-induced gut leakiness.1,6,7