Each doctor in the field of functional medicine can share tales about the ‘probiotic miracle’ – instances where patients, often suffering from severe, obsessive-compulsive spectrum symptoms, saw complete remission after changing their diets and adding probiotic supplements. Is this some sort of mystic phenomenon, or is it backed by a growing comprehension of the microbiome’s influence on mental health and behavior?
For the last twenty years, groundbreaking researchers have been validating inflammatory models of mental disorders like depression, bipolar disorder, and schizophrenia. Studies have concentrated on markers indicating immune distress in a significant subset of patients, a majority of whom are classified as “treatment resistant”. Through this research, we have discovered that depression can be induced in both animals and humans by inflammatory agents. It’s also been found that depression has a linear correlation with blood levels of inflammatory markers, meaning more markers equate to worse depression. Moreover, symptoms can be alleviated using pharmaceutical anti-inflammatories.
The gut’s role in inflammatory models of mental illness
Given this information, where should we start when we’re considering natural ways to modify the body’s inflammatory states? The answer is the gut, which houses over 70% of our immune system. The gut is our intermediary between the outside and inside worlds, separated by a single layer of cells. The resident microorganisms in our gut, outnumbering our human body cells by a ratio of 10:1, form an ecosystem through exposure to the postnatal environment, including the vaginal canal, breastfeeding, and our immediate surroundings. Disruptions to this bacterial balance from medications, gluten, herbicides, stress, and infections can prime our innate immune system for attack. Depression, which is linked with compromised integrity of this intestinal barrier, becomes a maelstrom of inflammation, cellular machinery impairment (e.g. mitochondria), oxidative stress, and more inflammation in a continuous cycle. Specifically, depression is linked with increased levels of lipopolysaccharide (LPS), an inflammatory toxin produced by bacteria that are supposed to stay within the gut.
If depression is a collection of symptoms driven downstream by inflammation, oxidative stress, and mitochondrial dysfunction, what lies at the source? Data from both animals and humans suggest that disruptions to our gut ecology may be a major contributor, bringing the microbiome into the spotlight of advanced psychiatric research.
The term “psychobiotics” refers to a live organism that, when consumed in sufficient amounts, provides a health benefit for patients suffering from psychiatric illness. A review by Dinan and others provides the clinical basis for using probiotics in mental health, referencing animal studies where behavioral changes were observed after exposure to certain bacterial strains like bifidobacterium and lactobacillus. In placebo-controlled trials in humans, it was shown to reduce symptoms of anxiety, chronic fatigue, and depression and anxiety associated with irritable bowel syndrome.
The clinical application of probiotics has been restricted to only a few strains out of the more than 7000 identified. It seems that colonization is not a standard outcome of probiotic supplementation, and it’s thought that genomic communication between bacteria and immune receptors may account for the anti-inflammatory effects.
Ancient knowledge
Considering our limited knowledge about the therapeutic applications of different strains, it may be prudent to rely on ancestral practices that underscore the significance of probiotic exposure. Traditional fermented foods like kimchi, pickles, sauerkraut, and other vegetables are examples where microbes interact with the food, and in turn, the food acts on our microbes.
So, what exactly do bacteria do in the gut? Is their role solely related to digestion? According to Selhub and others, they are involved in:
- Protecting the intestinal barrier;
- Influencing local and systemic antioxidant status, reducing lipid peroxidation;
- Directly producing neurochemicals like gamma-aminobutyric acid (GABA);
- Indirectly affecting neurotransmitter or neuropeptide production;
- Preventing stress-induced alterations to the overall intestinal microbiota;
- Directly activating neural pathways between the gut and brain;
- Limiting the production of inflammatory cytokines;
- Modulating neurotrophic chemicals, including brain-derived neurotrophic factor;
- Limiting carbohydrate malabsorption;
- Improving nutritional status, for instance, omega-3 fatty acids, minerals, dietary phytochemicals;
- Limiting small intestinal bacterial overgrowth;
- Reducing the burden of amine or uremic toxins;
- Limiting gastric or intestinal pathogens (like Helicobacter pylori);
- Providing analgesic properties.
Given the widespread practice of fermentation in traditional cultures, it seems that this dietary wisdom may help reduce gut-based inflammation and optimize nutrient absorption. One review noted significant reductions (38%) in blood LPS levels after one-month adherence to a traditional diet, while a Western diet provoked an increase in LPS levels.
In addition to enhancing the bioavailability and production of minerals, neurochemicals, and fatty acids, fermented foods also generate methylfolate, an activated form of folate required for methylation, brain chemical synthesis, detox, and gene expression.
Because of the intricate co-evolution of bacterial strains, cultivated through our food supply and complementing our internal microbiomes, we have the opportunity to use therapeutic foods to reeducate our immune system that has been led astray. Psychobiotics could potentially influence multiple factors at once.
This could manifest behaviorally via increased antioxidant and anti-inflammatory activity, reduced intestinal permeability and the harmful effects of LPS, improved glycemic control, positive influence on nutritional status (thereby affecting neurotransmission and neuropeptide production), direct production of GABA, and other bioactive chemicals. It may also directly influence gut-to-brain communication by beneficially shifting the intestinal microbiota itself.
It’s therefore persuasive to contemplate the power of reconnecting with nature through our food, signaling to our brains through our guts that nutrients are abundant, our bodies are safe, and that our inflammatory systems can relax. In these conditions, the complex interplay of the endocrine, immune, and gastrointestinal systems can proceed unhindered, supporting mental health and wellness.