Gut-Brain Axis


Special Series: Brain Waves

Bacteria on the Mind

By David Kattenburg

You are what you eat — so the saying goes. In fact, the trillions of bacteria inhabiting your gut also eat what you eat, and turn meals into molecules that affect your brain.

The gut-brain axis, it’s called. It can be positive and healthy, or — in the case of Crohn’s and other forms of Inflammatory Bowel Disease — an axis of evil. An estimated one out of 150 Canadians suffer from Crohn’s.

One of these is John Harvie.


“The pains were so tremendous,” the trim, healthy-looking Harvie recalls, sitting at a Winnipeg cafe. “You spend most of the day on the toilet.”

Crohn’s laid waste to Harvie’s life. Not surprisingly, it also wreaked havoc on his state of mind.

“At my lowest point I remember lying in a bathtub filled with water and thinking, okay, well, this is where I’ll open up my wrists.”

Dr. Charles Bernstein

Dr. Charles Bernstein

It’s a no-brainer. Painful and embarrassing gut problems are an emotional bummer. For Dr. Charles Bernstein, there’s more to it than that. Bernstein – a professor of gastroenterology at the University of Manitoba – has noticed that mood disorders in people with Crohn’s and other forms of Inflammatory Bowel Disease often precede gut problems. Bernstein thinks the trillions of bacteria in a person’s bowels affect both mood and gut function.

“Having bacteria in your bowel triggers an immune response,” says Bernstein. “If the trigger is an aberrant immune response, some of that immune response may also impact on brain function. By manipulating the bugs in the bowel, one may be able to improve the mood disorder.”

The idea of treating Crohn’s and its mood sequelae by manipulating gut bacteria intrigues Stephen Collins, a gastroenterologist at McMaster University, in Hamilton, Ontario. Bacteria are tiny chemical factories, Collins reasons.


Premysl Bercik and Stephen Collins

“The secretion of metabolites or some product of the bacteria either directly influences the brain or indirectly influences the brain,” says Collins. “Another way is by accessing neural circuitry directly, close to the inner surface of the gut.”

If healthy gut bacteria affect the mind, says Premsyl Bercik, a colleague of Collins at McMaster, it’s no surprise antibiotics can mess up a person’s head: “This is called antibiotic-induced psychosis, and usually these patients normalize their behavior when you stop this antibiotic treatment.”

Conversely, Inflammatory Bowel Disease and associated mood disorders both seem to be linked to abnormal populations of gut bacteria. The efficacy of probiotics – edible formulations of good bugs to replace the bad – is now under investigation. The simplest approach may be a healthy diet … for you and your gut bacteria.

“Diet is one of the major influences on the metabolic activity of the bacteria,” says Stephen Collins. “And if you now believe that these bacteria are in constant communication with the brain, then it’s absolutely possible, then, that food can alter your mood and your mental status via the microbiota.”

brainFor John Harvie, it makes perfect sense. “I don’t want to say that I have an understanding of the bacteria in my gut, but I will say that I have an understanding that if I eat a balanced meal, my mood is much better,” he laughs.

And probiotics? Harvie hasn’t tried them yet, but he’s open.

“I guess it’s like kick starting your bowel, to aid in digestion. And quite frankly, when you’re healthy your mood does improve. I can testify to that, and will all day long!”

If a good diet, anti-inflammatory drugs and probiotics don’t resolve a case of Crohn’s – and associated depression – a fecal transplant may be next. A potentially hazardous manoeuvre. Blood transfusions were considered perfectly safe until the emergence of blood-borne pathogens like HIV and Hep-C. Great care will be taken before inserting one person’s fecal matter into the gut of another, lest it cause infection – or go to their head.