Our bodies are inhabited by 100 times more microbes than our own human cells. These microbes live on our skin, in our mouths, our sinuses, the respiratory tract, vaginal canal – everywhere in our body. The majority of these microbes live in our intestines where they get a delivery of food several times a day.
Modern technology (such as genetic sequencing) has allowed us only in the past few decades to study these microbes and we continue to learn something new about them every day. It has become clear that these microbes and their metabolites have a profound effect on our health: our digestive health, immune health, metabolism and even our brain health.
Our microbiome is shaped by the way we are born, our lifestyle (exposure to animals, time spent outdoors, level of physical activity, stress levels), medications, but mostly – our diet. Beneficial bacteria (probiotics) with positive effects on mental health are called “psychobiotics”. These are beneficial bacteria such as Lactobacilli and Bifidobacteria (often present in fermented foods and probiotic supplements), that are calming to our immune system (anti-inflammatory) but also synthetize calming neurotransmitters such as GABA (gama-amino-butyric acid) and BDNF (brain derived neurotrophic factor), which is crucial for learning and memory. Volunteers in a study that were given probiotics reported less subjective low mood and distress and had lower stress hormone (cortisol) levels and less activation of the brain (measured by functional MRI) in response to emotional images compared to a placebo group. In another study – prebiotics (fiber) – given to healthy volunteers resulted in less reactivity to negative emotions and attenuated vigilance (marker of anti-depressant and anti-anxiety effect).
Besides production of neurotransmitters, psychobiotics exert their beneficial effect on the brain via direct stimulation of the nervous system in the intestine (the enteric nervous system) and the vagal nerve. Stimulation of vagal nerve exerts anti-inflammatory effect and vagal stimulation devices are used therapeutically for severe depression non-responsive to medications, for pain and even for epilepsy.
Yet, we can all have more vagal stimulation though the right kind of diet promoting healthy microbiome.
Whatever we eat feeds not only us, but also our gut microbiota. Moreover, microbes in our gut are capable of fermenting the fiber in our food that we could not digest ourselves and producing a variety of compounds from it (metabolites). These metabolites (sometimes called “postbiotics”) get absorbed from the intestine and have a major impact on our health, including our brains. Some bacterial metabolites are good for our health, but some are harmful, or downright toxic.
One of the most dramatic examples of intestinal bacteria on our brain is hepatic encephalopathy, a condition related to poor liver clearance of intestinal bacterial toxins in patients with cirrhosis, that can result in a coma. These patients, essentially “poisoned” by their own gut, “wake up” from their coma after administration of antibiotics “overnight”.
But many of us may be “intoxicated” from our own guts in a more subtle fashion - perhaps experiencing brain fog, fatigue, or depression, anxiety or difficulty focusing.
The “bad” kinds of bacteria and inflammatory cytokines are promoted by the SAD (Standard American) diet, which is high in sugar, fat and salt from processed foods, and low in fiber from nuts, seeds, fruits and vegetables. Besides the different bacterial metabolites (measurable in our blood), we can also measure elevated levels of bacterial lipopolysaccharide (LPS) in people on Western SAD diet. People with high LPS in their blood are more likely to suffer from depression as well as Alzheimer’s dementia. The Western diet is more likely to cause inflammation. Inflammatory mediators (such as cytokines and interleukins) have negative a impact on our brain and have been linked to depression, anxiety, hostility as well as cognitive decline.
Changes in gut microbiome have been found even in children with autism. Treatment of autistic children with fecal transplant resulted in significant improvement in their behavior and brain development which persisted even 5 years after the study was completed.
There are striking differences between different countries in the number of autistic children – quite possibly reflecting at least partially the different dietary habits.
Fecal transplants done for Clostridium difficile have often resulted in a cure of pre-existing depression, and people being able to discontinue anti-depressants that they have been taking for years.
Besides direct effect of our food on our microbiome, we have also allowed thousands of additives and artificial ingredients, such as non-caloric sweeteners, to get into our food, and labeled them as safe before we understood the impact they would have on our microbiome. We now know that artificial sweeteners can be metabolized by our intestinal microbes and converted not only into energy (contributing to the epidemic of obesity and diabetes) but also into harmful substances with negative impact on the intestine as well as the brain. Sucralose (Splenda) is used in laboratory animals to induce Crohn’s disease. Rotenone (an “organic” pesticide) is used to induce Parkinson’s disease in laboratory mice, so we can study the disease. The more commonly used pesticide Glyphosate (Round-up) has a detrimental effect on our gut microbiome (similar to antibiotics) and produces changes in the intestinal lining reminiscent of celiac disease (extreme form of gluten sensitivity). Both celiac disease and non-celiac wheat sensitivity have been on the rise and have now reached epidemic proportions as well.
Artificially sweetened beverages have been linked to a higher risk of depression, same for coffee sweetened with artificial sweeteners (although unsweetened coffee significantly lowers risk of depression and suicide). Aspartame (Equal) is metabolized in the gut to phenylalanine, aspartic acid and methanol, altering the brain neurotransmitters dopamine and serotonin and resulting changes in mood and behavior. People with pre-existing depression may be more vulnerable to the negative effect of Aspartame. While animal research has deemed aspartame as safe, a study of aspartame in people with pre-existing depression showed such severe disturbances in their mood and behavior it had to stopped early (it was deemed unethical to continue).
Along with over 2,000 additives in our diet, there are hundreds of contaminants such as pesticide residues, antibiotics, hormones and hormone mimicking (endocrine disrupting) chemicals. Endocrine disruptors are known to disrupt normal brain development, sex specific development, stress response and behavior. These chemicals leaching into our food from plastic packaging, pesticide, fungicides and herbicides, have been shown to disrupt the synthesis, transport and release of neurotransmitters, affecting our cognition, learning, memory and behavior. Mixtures of chemicals often have an augmented, synergistic effect.
Over the past 50 years, many health issues have reached epidemic proportions. One out of 50 children suffer from autism, 40% of population will at some point experience either anxiety, depression or attention deficit disorder and many will succumb to Alzheimer’s dementia. Parkinson’s disease, multiple sclerosis and ALS are also on the rise.
Our microbiome, along with environmental pollution, contribute to these epidemics significantly. It is up to us to create a healthier future for ourselves.
