“All disease begins in the gut” is a quote from the ancient Greek physician Hippocrates, who lived 2,500 years ago. As scientists and medical experts learn more about gut health, the microbiome, and disease, it appears that Hippocrates’ assertion was quite accurate.

1. Gut-Brain-Axis and the Vagus Nerve

There is a great deal of interest and research on the importance of the microbiome and its impact on health. We have all experienced that strange feeling of butterflies in our stomach when we are doing something new and exciting or when we are nervous. This feeling occurs because there is a direct connection between our gut and our brain. This is referred to as the gut-brain-axis (GBA). The GBA is best described as a two-way communication between the gut and brain.

Messages are sent from the gut via 500 million neurons that reside in the gut through the vagus nerve. The vagus nerve is the longest nerve of the autonomic nervous system – the portion of the nervous system that controls automatic physiological responses, like heartbeat and digestion. The vagus nerve’s fibers run from the gut to the base of the brain, and the messaging is bi-directional – the messaging goes each way between the gut and the brain.

2. Gut Permeability

How does having what’s referred to as a “leaky gut” affect the brain? The gut’s mucosal cells are held together like glue by so-called “tight junctions.” Tight junctions are proteins that have receptors. When these tight junctions become “leaky” – or abnormally permeable – food particles and undesirable substances can leak into the circulatory system that can cause increased inflammation and inappropriate immune responses. The medical community believes that many chronic diseases can arise from the imbalances associated with gut permeability issues. For example, excess gut permeability can impact mood disorders, neurodegenerative diseases, and even autism.1

Some species of beneficial bacteria can protect the gut barrier from becoming leaky. An example is Lactobacillus rhamnosus, which is associated with increased barrier function and expression of the tight junction proteins, as well as decreased serum inflammatory cytokines. On the other hand, the overgrowth of Clostridium spp. is associated with intestinal microbial dysbiosis, which can lead to leaky gut syndrome and other immune-related disorders.2

3. Dysbiosis

As is readily perceived from the foregoing, many systems in the body are interconnected. The microbes in the gut and their genes and metabolites help support balance throughout the body. The microbiome aids in the development of the immune system and can be a predictor of future health or disease. The multiple and various beneficial organisms in the gut can prevent the invasion of pathogenic organisms, contribute to the fermentation of non-digestive fibers, help produce vitamins, and are involved in metabolism of short-chain fatty acids and carbohydrates. These organisms assist the body in absorbing minerals and regulating inflammatory processes.

We used to think of the blood-brain barrier (BBB) as an impermeable barrier that protected the central nervous system and brain from bacteria, toxins, and other intruders. We now know the BBB can be breached, and there is growing evidence that changes in the microbiome are associated with BBB permeability.

When pathogenic bacteria replace healthy bacteria, gut dysbiosis can ensue. The gut microbiome in the case of dysbiosis can have a very different metabolic profile than a healthy microbiome. For example, studies show that the composition of the gut microbiome of an individual with mild cognitive impairment (MCI), an early stage of Alzheimer’s disease and other forms of dementia, is different from that of individuals without MCI. Recent studies suggest that the gut microbiome might also contribute to the development of other neurodegenerative diseases, such as Parkinson’s disease, psychiatric diseases, and stroke.3 Changes in the gut-brain axis have also been associated with autism spectrum disorder (ASD). Studies show that gastrointestinal problems are 23-70 percent more prevalent in ASD children.  Children with ASD and GI problems also have more behavioral problems overall.4

Much of the Research is Preliminary

Most of the information that supports the connection between the gut microbiome and brain function has come from animal studies. In some studies, researchers took germ-free mice (mice with no microorganisms in them or on them) and evaluated their brain structure and function prior to and after exposure and colonization of the gut with bacteria. The studies show that the germ-free rodents had structural alterations in the blood-brain barrier, with the tight junctions not being as pronounced or efficient, giving rise to BBB permeability compared to the conventional mice with intact microbiomes.2  The research has also found that when germ-free mice are given fecal transplants their BBB permeability decreases.

Similar studies looking at mice that had long-term antibiotic use found these mice had impaired object recognition and decreased hippocampal neurogenesis and memory retention. Once these mice were given probiotics, the adverse changes in cognition reversed.2

When trying to identify modifiable risk factors for cognitive decline, we currently know that hypertension, diabetes, atherosclerosis, obesity, and hypercholesterolemia are among the most significant risk factors for cognitive decline. With the connection between cognitive decline and these chronic metabolic diseases, research is shifting to looking at dietary and lifestyle influences that impact the microbiome.

The Takeaway

What else can be done to support a healthy microbiome – and ultimately brain health? Taking a prebiotic supplement and/or a probiotic supplement are good places to start.* In addition, emphasis should be given to a nutrient dense, whole-food diet – less fast food and processed foods. Likewise, focus should be given to managing stress, maintaining regular sleep habits, and getting regular exercise. Thankfully, many factors that impact our health are within our own grasp when we commit to healthy lifestyle changes.

For a more personalized approach to your gut health, consider Thorne’s Gut Health Test. This test provides a detailed analysis and personalized plan of diet, lifestyle, and supplement recommendations. Collect your sample with our revolutionary wipe technology in the comfort of your own home. 

References

  1. Morais LH, Schreiber HL, Mazmanian SK. The gut microbiota-brain axis in behaviour and brain disorders. Nat Rev Microbiol 2021;19:179-194.
  2. Parker A, Fonseca S, Carding SR. Gut microbes and metabolites as modulators of blood-brain barrier integrity and brain health. Gut Microbes 2020;11(2):135-157. doi: 10.1080/19490976.2019.1638722.
  3. Forssberg H. Microbiome programming of brain development: implications for neurodevelopmental disorders. Dev Med Child Neurol 2019;61(7):744-749. doi: 10.1111/dmcn.14208. 
  4. Yitik-Tonkaz G, Esin IS, Turan B, et al. Determinants of leaky gut and gut microbiota differences in children with autism spectrum disorder and their siblings. J Autism Dev Disord2022 Apr 20. doi: 10.1007/s10803-022-05540-z.