If you have ever been truly disgusted by something you saw, you have experienced feeling sick to your stomach. Revulsion involves the brain, clearly, but somehow it can be felt in our digestive system. The same is true of anxiety and love: there’s a reason we speak of butterflies in our stomach.
To the probing minds of our ancestors, the stomach was mysterious. Unlike the mouth or the eye, it couldn’t be easily accessed and studied. An unfortunate musket shot would change that.
That shot was heard on June 6, 1822, and its victim was a French-Canadian named Alexis St-Martin (whose name is often anglicized to St. Martin). Modern accounts of the incident disagree on how old he was, placing him somewhere between the ages of 18 and 20. He was a coureur des bois, a “runner of the woods” tasked with trading with First Nations people. St-Martin was on Mackinac Island (in present-day Michigan), at an annual pelt swapping jamboree, waiting in line, when the shotgun was . The injury was so severe, his doctor didn’t think he would survive.
Said doctor was William Beaumont, a military officer who had served as a surgeon’s mate in the War of 1812. Beaumont tended to St-Martin, who had a gaping wound in his chest through which his breakfast poured out. As the wound healed over the course of nine months, something peculiar happened. The stomach had fused to the wall of St-Martin’s chest, creating a valve. In case you want a more vivid mental image and don’t mind the accompanying stomach-churning feeling, Beaumont : that the healing process “left the perforation resembling, in all but a sphincter, the natural anus.”
At the time, the way in which the body digested food was still mired in mystery and speculations. Beaumont, who would go on to be remembered as the father of American physiology, saw an opportunity to shed light on this process. Over the course of ten years, Beaumont would conduct experiments on St-Martin, introducing food through the sphincter-like mouth and into the man’s stomach and pulling it out with a string at various time points. He would also collect stomach juices during digestion and test them. The ethics of this research have been : no formal code for medical experimentations existed at the time, and so the two men discussed their relationship as a sort of employment contract, with St-Martin acting as a domestic servant. On multiple occasions, St-Martin fled and returned to Canada, with Beaumont ultimately convincing him to come back to the United States for more painful experiments in exchange for wages, care, room, and board.
Because of the  Beaumont performed on his patient, we learned that, as had been hypothesized, the acid secreted by the stomach is indeed hydrochloric acid, and that digestion is helped by the warmth and motion of the stomach itself. But in the middle of all this, Beaumont also made note of how emotions were associated with digestion.
It only happened , in March of 1831. When St-Martin expressed “violent anger” during one of the experiments, Beaumont noted the presence of yellow bile in the man’s stomach, which was not supposed to be there. The bile, produced in a lower part of the digestive tract, had moved up via reflux to enter the stomach. Two days later, in another test, Beaumont would witness delayed digestion and attribute it to his patient’s anger and impatience.
In the 1900s, scientists here and there would continue to look at how emotions could affect digestion, with some describing more gastric secretions and a reddening of the inside of the stomach following excitement, anger or pleasure. Fear and depression were seen as having the opposite effect.
But accessing the stomach for these types of studies often depended on finding the rare person whose anatomy, through birth or surgery, allowed a doctor easier access to the famed organ.
Thanks to technology, this is no longer the case.
A fantastic voyage inside the gut
The results of  were just published, in which Italian researchers wanted to see what happened inside the stomach when participants were shown video clips eliciting a range of strong emotions. It turns out that disgusting and fear-inducing material was associated with a more acidic pH inside the stomach. How did they measure this? Using a tiny probe the participants swallowed.
It's called the SmartPill. You can think of it as a miniaturized version of the Mars Rover. This polyurethane cylinder is a little over 2.5 cm long and has a battery that lasts at least five days. As it travels through your digestive tract, it can measure pH, temperature, and pressure. These measurements can be used to infer where along the gut the SmartPill is. When it enters the stomach from the esophagus, temperatures rise and pH drops. As it enters the small intestine, the pH becomes more basic by at least two units. In the colon, the pH becomes a bit more acidic, and when the temperature drops drastically and the signal is lost, it means the capsule was evacuated. Down the toilet it goes, but thankfully its precious information was transmitted in real time to a receiver. Analyzing it can be useful for doctors stumped by patients who have a delayed emptying of their stomach or chronic constipation.
The SmartPill was developed by a company in Buffalo, New York, and cleared by the Food and Drug Administration in 2006 for the above medical issues. In 2012, it was sold to an Israeli imaging firm, which was subsequently purchased by Medtronic. While the capsule was available for purchase, a number of studies were done making use of it, leading to a better understanding of how our digestive tract works, much like Beaumont had done in the 1800s (minus the discomfort and the questionable ethics). Last year, though, the SmartPill was  because its maker could not reliably get their hands on the necessary supplies to make some of its critical components. Before it stopped being sold, though, an Italian team got a hold of it to see exactly what happens when we say we’re sick to our stomach.
Their 31 young healthy participants did not know the exact purpose of the experiment in the beginning. They were all given the same breakfast: egg whites and two slices of bread and jam. They swallowed the SmartPill in front of a researcher and leaned back for the start of the test. When the pill was confirmed to have been in their stomach for at least 15 minutes, they began viewing soundless video clips broken down into blocks. Each block was meant to elicit a specific emotion: disgust, fear, happiness, and sadness, with a fifth block consisting of neutral footage meant to serve as a control.
We often hear that we have become desensitized to violence because of cinema and video games. The researchers must have been aware of this, because the clips they chose to cause disgust in their participants sound particularly vile. You can skip to the next paragraph if you don’t want to become an unwitting participant in this study. There was a clip of a man taking off his own fingernail. In another one, a man smells a bowl of vomit and drinks it. If that’s not enough, there’s always the clip described as “a man is covered with faecal matter.” Suffice to say, the researchers didn’t hold back.
After confirming in multiple ways that the clips were indeed eliciting the emotion they were meant to, they looked at the measurements. There was no accompanying association with anything measured in the small intestine, be it pH, pressure, or temperature. But the stomach got more acidic when the person experienced fear or disgust.
This is one more study to add to the small canon of experiments demonstrating a link between our emotions and our digestion and giving us a glimpse into how emotions are processed in the body. This is not definitive, though. The study only recruited men, to avoid any potential variation due to sex, and it’s unclear if the emotions made the stomach more acidic or if the increased acidity is what is transformed into the sensation of fear or disgust by the brain. In future experiments, the scientists would like to provoke strong emotions in their participants and counteract, in real time, this increased acidity with antacids to see what happens.
We have developed a very inventive language when it comes to our gut. We often refer to it as a second brain, where butterflies make a rumble and where gut feelings tell us what’s really going on. There is a grain of truth once we use science to probe the seven-to-nine metres of gastrointestinal tract we possess. We can strip away the more outlandish claims by taking careful measurements and figure out exactly how our feelings impact our gut and vice versa.
We can do it by dunking food into the stomach via gunshot wound, but we can also do it by building interplanetary probes and shrinking them down until they can be swallowed and ejected at the end of their transit.
The inventiveness of scientists can certainly give us food for thought.
Take-home message:
- A new study using a swallowable probe provides evidence that the stomach gets more acidic when we experience fear or disgust
