Moods, Microbes, and Digestion

When Alexis St. Martin is accidently shot in the stomach while working in the American Fur Company store in Mackinac Island in 1822, surely he believes the end is near. As the doctor rushes to the scene, a crowd of aghast fur traders and store clerks watches as the unfortunate victim’s partially-digested breakfast seeps from a hand-sized wound in his stomach. Most believe that the man is doomed. Little do they know that St. Martin is about to become the most famous human Guinea pig in recorded history and the subject of a multi-year experiment that will lead to the discovery of digestive enzymes and provide extraordinary insight into the workings of a living, fully-functional human digestive tract.

Dr. William Beaumont, the Army surgeon at Fort Mackinac, works feverishly to stop the bleeding and repair the damage. He cleans the wound, clips off pieces of a rib with a penknife to ease back a portion of a protruding lung and then applies poultice. After several days of severe fever and pneumonia, St. Martin begins to feel better and after six months under the care of Beaumont, he makes a miraculous recovery, with one exception. Despite Beaumont’s attempts, the hole in St. Martin’s stomach does not heal and a gastric fistula forms, creating a permanent opening to the man’s stomach and its contents.

Being a curious man, Dr. Beaumont peers into the coin-sized opening in St. Martin’s body and comes to the astonishing realization that this hole, perfectly formed and mended, provides a unique view into the workings of a living human stomach. Soon after, Beaumont begins his experiments. He spoon-feeds the opening and then siphons out the contents to study the effects. He attaches meat to a string, stuffs it through the hole and then pulls it back out for observation. Before long, he disproves the leading notion at the time that digestion in the stomach is a mechanical process. Rather, he concludes in his much acclaimed book, “Experiments and Observations of the Gastric Juice and Physiology of Digestion”, that the digestive process occurs through chemical means, largely the result of hydrochloric acid and other gastric juices.

Beaumont’s amazing discoveries didn’t end with the identification of gastric juices. The living, fully-functional stomach of Alexis St. Martin soon begins giving up secrets that had been hidden from view since the beginning of human history. As the good doctor prods and fiddles inside St. Martin’s stomach with spoons, clunky thermometers and other measuring devices, the subject begins to exhibit unusual mood changes. Beaumont expected to observe temporary pain reflexes, nausea and dizziness as a result of his ongoing work but the long-term changes in mood is an unexpected finding that he takes great care to describe in his book. What’s more, the mood changes seem to be bi-directional, meaning that observed changes in emotional state often lead to changes in gastric function and vice versa.

Beaumont’s experiments are believed to be one of the first documented accounts of the bi-directional communication between the brain and the gut. Of course the primal connection between the gut and brain has been surmised for centuries. Over two thousand years ago Hippocrates, known as the founder of medicine, stated that “all disease begins in the gut”. At young ages, we’ve all been taught to “trust our gut instinct” and how often have you heard someone say they have a “gut feeling” about something or someone? The “butterflies in my stomach” comment is not just a metaphor to describe a nerve-wracking situation, these “feelings” have a physiological basis that involves extensive networks of neurons and chemical signals that connect the brain to the gut and vice versa.

Modern science describes the hundreds of millions of neurons connecting the digestive system to critical bodily functions as the enteric nervous system. In fact, the enteric nervous system is so expansive that it can operate independently from the central nervous system and has been called the “second brain”. While the enteric nervous system is tasked with ensuring proper digestive function, its role in human physiology goes much further. It controls local blood flow, motor functions, mucosal transport and secretions, and modulates immune and endocrine functions. Amazingly, recent studies have revealed an interplay between the enteric nervous system, the brain and our environment that would have astounded the likes of William Beaumont; it seems that the millions of neurons in our gut not only regulates critical bodily functions, but they also listen and take cues from the trillions of microbes residing in our intestines.

Scientists are only beginning to decipher the complexed messages that our gut microbes are delivering to our brain via the enteric nervous system. It turns out that our Central Nervous System (i.e., composed of neurons in the brain and spinal cord) and our Enteric Nervous System are connected primarily by a bi-directional signaling pathway known as the vagus nerve (i.e. the parasympathetic nervous system). This bi-directional pathway is considerably one-sided since as much as 90% of the messages traveling along the vagus nerve go from the gut (i.e., enteric nervous system) to the brain. This means that the brain is in constant communication with our Enteric Nervous System, which in turn, is continually listening to the mass of microbes residing in our gut.

It may be difficult to imagine that our emotions and moods are influenced by microbial activity going on inside our intestines, but recent scientific literature is rich in evidence demonstrating a powerful link between the two. For instance, Bercik and colleagues carried out experiments in mice showing that is possible to transfer behavioral traits using fecal transplantation. Specifically, they showed that fecal microbiota transplants from an anxious mouse produces anxious behavior in the recipient while transplants from a non-anxious mouse produces non-anxious behavior. The behavioral transfer brought on by the transplants also altered brain chemistry suggesting that fecal microbiota transplantation, or other therapeutic tools that alters the gut microbiota, may someday be used to treat disorders such as depression or anxiety.

While it’s fascinating to consider that gut flora alterations may improve moods and emotions, science is still a long way from understanding the exact role that gut microbes play in modulating our feelings. By providing the above example, I’m not suggesting that people rush out to get fecal microbiota transplants to correct mood disorders but there are actions that we all can take to improve the status of our gut flora.

Like all ecosystems inhabited by competing species, the environment in the gut dictates which species and strains of microbes thrive. In past blogs I have presented examples of scientific experiments demonstrating the positive health benefits of increased diversity within gut microbiota populations. When we eat processed foods with high sugar content we are destroying diversity within our gut flora by providing a competitive advantage to microorganisms that promote deleterious effects on our health such as inflammation and obesity. Consequently, it is good to stay away from sugary foods and drinks since the bad microorganisms in your gut thrive on these unhealthy foods.

The best way to promote a diverse gut microbiota is to eat a diverse diet containing plenty of vegetables and fruits that contain prebiotic fiber. You should also consume probiotic-containing foods such as yoghurt, kefir, and fermented vegetables. I also believe that it is important to consume high quality probiotic supplements on a daily basis with a diverse set of beneficial bacteria to keep the bad actors in check.

There are numerous scientific articles showing that the intake of probiotics can help reduce negative thoughts associated with sad moods. For example, Steenbergen et.al., demonstrated that a group of 20 healthy people who took a multispecies probiotic containing Bifidobacterium and Lactobacillus species over a 4-week period of time showed a significantly reduced cognitive reactivity to sad mood (i.e., accounted for by reduced rumination and aggressive thoughts) compared to a control group that took an inert placebo. There is a good reason for this since 80-90% of the potent neurotransmitter, serotonin, is found primarily in the intestines and the microorganisms in the gut play a central role in regulating serotonin through the metabolism of the amino acid, tryptophan. Serotonin regulates feelings of happiness and some of the most prescribed anti-anxiety and anti-depression drugs such as Prozac and Zoloft work by modulating serotonin levels.

Science has come a long way since the ghastly experiments conducted on Alexis St. Martin’s body in deciphering the link between our digestive system and our feelings. The experiments on St. Martin’s body lasted for over ten years, during which time, Dr. William Beaumont was reassigned to posts in Wisconsin, New York and Washington D.C. In order to carry on with his “work”, Beaumont found ways to entice his subject to remain close, usually by hiring him as a chore boy and hired hand. As the accolades for Beaumont’s ground-breaking work poured in from the United States and beyond, the relationship between the two men soured. In his writings, Beaumont described his subject as a “villain”, “drunkard” and “ungrateful” even though the experiments often left St. Martin nauseous and constipated with severe headaches. When St. Martin left Beaumont to go back to Canada to be with his beloved wife and children, Beaumont wrote that his subject had “absconded”.

In today’s society where the civil rights of an individual trumps all other considerations, it’s difficult to understand how Beaumont and the larger scientific community of the day justified the inhuman treatment of Alexis St. Martin. It’s clear that Beaumont and his peers believed that the end justified the means and dismissed all ethical arguments without the slightest hint of compassion for the human subject. Indeed, it appears that history has looked kindly on William Beaumont and despite the means by which he accomplished his work, today he is celebrated as the Father of American Physiology. As for Alexis St. Martin, we do not know why he agreed to offer his body up to science. It’s most likely that he needed a job after the debilitating injury and likewise felt an obligation toward Dr. Beaumont for saving his life. Regardless of his motivation, St. Martin’s sacrifice was significant and his contribution should be celebrated alongside his physician, William Beaumont.

Other Resources:

Collins S.M., et. al., The adoptive transfer of behavioral phenotype via the intestinal microbiota; experimental evidence and clinical implication. Curr. Opin. Microbiol. 2013. 16(3):240-245.

Steenbergen et. al., A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain Behav. Imm. 2015. 48:258-264.

About the author:

Douglas Toal, PhD is a Microbiologist with extensive knowledge and expertise in medical and environmental microbiology with additional training in metabolism and anti-aging medicine. He is founder and Chief Scientific Officer of Liberty Bion, Inc.

At Liberty Bion, Inc. our mission is to deliver quality natural supplements, healthy living strategies, and innovative educational tools that promotes good health and adds value to the lives of our customers. Our Hero ProbioticsTM brand is formulated to support your effort to create a diverse microbiota by delivering 30 billion CFUs of 10 diverse and beneficial probiotic strains per serving. 

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