Your Brain is Changed by What Happens in Your Gut

From When Gut Bacteria Change Brain Function:

“By now, the idea that gut bacteria affect a person’s health is not revolutionary. Many people know that these microbes influence digestion, allergies, and metabolism. The trend has become almost commonplace: New books appear regularly detailing precisely which diet will lead to optimum bacterial health.

But these microbes’ reach may extend much further, into the human brains. A growing group of researchers around the world are investigating how the microbiome, as this bacterial ecosystem is known, regulates how people think and feel. Scientists have found evidence that this assemblage — about a thousand different species of bacteria, trillions of cells that together weigh between one and three pounds — could play a crucial role in autism, anxiety, depression, and other disorders.

“There’s been an explosion of interest in the connections between the microbiome and the brain,” says Emeran Mayer, a gastroenterologist at the University of California, Los Angeles, who has been studying the topic for the past five years.

Some of the most intriguing work has been done on autism. For decades, doctors, parents, and researchers have noted that about three-quarters of people with autism also have some gastrointestinal abnormality, like digestive issues, food allergies, or gluten sensitivity. This recognition led scientists to examine potential connections between gut microbes and autism; several recent studies have found that autistic people’s microbiome differs significantly from control groups. The California Institute of Technology microbiologist Sarkis Mazmanian has focused on a common species called Bacteroides fragilis, which is seen in smaller quantities in some children with autism. In a paper published two years ago in the journal Cell, Mazmanian and several colleagues fed B. fragilis from humans to mice with symptoms similar to autism. The treatment altered the makeup of the animals’ microbiome, and more importantly, improved their behavior: They became less anxious, communicated more with other mice, and showed less repetitive behavior.”

From The Brain-Gut Connection:

“If you’ve ever “gone with your gut” to make a decision or felt “butterflies in your stomach” when nervous, you’re likely getting signals from an unexpected source: your second brain. Hidden in the walls of the digestive system, this “brain in your gut” is revolutionizing medicine’s understanding of the links between digestion, mood, health and even the way you think.

Scientists call this little brain the enteric nervous system (ENS). And it’s not so little. The ENS is two thin layers of more than 100 million nerve cells lining your gastrointestinal tract from esophagus to rectum.

What Does Your gut’s Brain Control?

Unlike the big brain in your skull, the ENS can’t balance your checkbook or compose a love note. “Its main role is controlling digestion, from swallowing to the release of enzymes that break down food to the control of blood flow that helps with nutrient absorption to elimination,” explains Jay Pasricha, M.D., director of the Johns Hopkins Center for Neurogastroenterology, whose research on the enteric nervous system has garnered international attention. “The enteric nervous system doesn’t seem capable of thought as we know it, but it communicates back and forth with our big brain — with profound results.”

The ENS may trigger big emotional shifts experienced by people coping with irritable bowel syndrome (IBS) and functional bowel problems such as constipation, diarrhea, bloating, pain and stomach upset. “For decades, researchers and doctors thought that anxiety and depression contributed to these problems. But our studies and others show that it may also be the other way around,” Pasricha says. Researchers are finding evidence that irritation in the gastrointestinal system may send signals to the central nervous system (CNS) that trigger mood changes.”

From The gut-brain connection:

“Given how closely the gut and brain interact, it becomes easier to understand why you might feel nauseated before giving a presentation, or feel intestinal pain during times of stress. That doesn’t mean, however, that functional gastrointestinal conditions are imagined or “all in your head.” Psychology combines with physical factors to cause pain and other bowel symptoms. Psychosocial factors influence the actual physiology of the gut, as well as symptoms. In other words, stress (or depression or other psychological factors) can affect movement and contractions of the GI tract.

In addition, many people with functional GI disorders perceive pain more acutely than other people do because their brains are more responsive to pain signals from the GI tract. Stress can make the existing pain seem even worse.

Based on these observations, you might expect that at least some patients with functional GI conditions might improve with therapy to reduce stress or treat anxiety or depression. Multiple studies have found that psychologically based approaches lead to greater improvement in digestive symptoms compared with only conventional medical treatment.”

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