The Mind-Gut Connection summary

The earliest writings of ancient humankind contain references to enemas. In Ancient Egypt, the pharaoh had a “keeper of the rectum” who managed all of his enemas. Ancient Babylonian and Assyrian tablets mention the use of enemas as early as 600 BC. Susrut, the father of Indian surgery, wrote details of implements he used to clean out the colon.

Why has humanity been obsessed with the state of the human gut for so long? The answer may lie in a quote credited to Hippocrates: “All disease begins in the gut.”

It turns out that Hippocrates wasn’t too far off in his thinking. We now know that immune cells located throughout the gut make up the largest part of the immune system. Not only that – the gut is equipped with its own dedicated nervous system that many people refer to as a second brain. And, as if that weren’t enough, the gut contains endocrine cells that hold 20 kinds of hormones and also contains the largest supply of serotonin in your body.

These systems don’t just hang out in the gut independently of the rest of the body. They communicate with the brain via the vagus nerve. So if you’ve ever had a “gut feeling” about something, that phrase is more than just a metaphor. You probably had a literal gut feeling.

Using this vagus nerve super highway, your brain receives tons of information from your gut every day, and stores that information in memories. Studies suggest that you’ll never be consciously aware of about 90 percent of that information, but it can and does affect how you behave in response to certain stimuli. Research has also found that 90 percent of the information transferred goes from gut to brain, and only ten percent from brain to gut. Think of the gut like an agent in the field sending intelligence back to head office.

So with all of this information at hand, it’s no wonder that researchers are speculating about the possibility of the gut’s role in the development of mental and emotional conditions like depression and anxiety.

In 1822, army surgeon Dr. William Beaumont was able to witness firsthand, in a bizarre way, the direct effect that emotions have on digestion. He treated a man named Alexis St. Martin, who had been accidentally shot through the stomach with a musket.

While Dr. Beaumont was able to help St. Martin regain function, he wasn’t able to permanently close up his stomach. As a result, there remained enough access to the stomach so that Dr. Beaumont could actually observe digestion in real time. With the consent of St. Martin, Dr. Beaumont studied the direct effects of emotional stimuli on digestive responses.

As the experiments were often uncomfortable for St. Martin, he frequently became upset during the process. By watching St. Martin’s gastric activity as his mood turned, Dr. Beaumont found that St. Martin’s anger ended up slowing his digestion. 

While Beaumont’s experiments showed how feelings affect digestion, later experiments showed how gut microbes affect behaviors. Scientists transplanted fecal microbes from one mouse into another and observed any changes in behavior. They found that a timid mouse injected with the microbes of an extroverted mouse became more extroverted. And a lean mouse injected with the microbes of an obese mouse changed its eating habits and gained weight.

This opens up a whole realm of speculation on the role gut microbes play in your feelings and behaviors, and what possibilities there may be in the future for gut-based therapies.