‘Gut Feelings’: More Than Heartburn, Indigestion?

Posted on Jul 29, 2015 in Chronic Disease, Medical Rewind

Listen to what Dr. Rashid A. Buttar and Robert Scott Bell have to say about this article on the June 8th Medical Rewind Show


If promising but early studies pan out, psychiatrists of the future could make a most unusual request of their patients: a sample of their stool.

Yes, the bodily specimen used to help diagnose digestive diseases might also offer clues as to what’s happening at the other end of someone’s anatomy.

Intriguing research, done mainly in rats and mice so far, suggests that bacteria that live in the gut influence brain development, mood, and behavior. Someday, doctors might be able to treat mood disorders with probiotics, supplements containing good gut bacteria; prebiotics, which promote the growth of good bacteria in the gut; or highly specific antibiotics that kill bad gut bacteria.

Depression “clearly isn’t all about Prozac and serotonin,” says Roger McIntyre, MD, who directs the Mood Disorders Psychopharmacology Unit at the University of Toronto. “We need to look at alternative explanations, alternative treatments.”

And at least for some people with a mental illness, a major contributing factor might be the 100 trillion bacteria — “aliens,” as Dartmouth microbiologist and immunologist Lloyd Kasper, MD, calls them — that live in the gut.

Scientists call this two-way street the gut-brain axis, and they’re just beginning to learn how the two organs talk with each other. “We’re so far at the tip of the iceberg on this that we don’t know where it’s going to go,” Kasper says.

Babies are born with sterile guts, but bacteria begin moving in within hours. The bacteria population remains relatively stable from age 3 onward, but things like environment, diet, drug exposure, and genetics can influence which ones thrive, McIntyre says.

Healthy people tend to have similar types and proportions of gut bacteria. Changes in the gut bacteria have been linked not only to digestive disorders but also to metabolic and brain disorders, says Jane Foster, PhD, an associate professor of psychiatry and behavioral neurosciences at McMaster University.

In an interview, Foster described several possible ways that gut bacteria and the brain communicate.

One is via the enteric nervous system, the part of the nervous system that governs the digestive tract. Also, gut bacteria can alter how the immune system works, which can affect the brain. The gut bacteria are involved in digestion, too, and the substances they make when they break down food can affect the brain.

And under certain conditions, such as stress or infection, potentially disease-causing gut bacteria, or bad bugs, can leak through the bowel wall and enter the bloodstream, enabling them and the chemicals they make to talk with the brain through cells in blood vessel walls. Bacteria could also communicate directly with cells in certain regions of the brain, including those located near areas involved in stress and mood, Foster says. It’s unclear, though, how that might affect your mood.