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At a downtown Toronto hospital researchers are testing a remarkable hypothesis — that transplanting poop from a healthy person could treat bipolar depression.

Dr. Valerie Taylor has people from around the world volunteering to be part of her pioneering clinical trial.

"The goal is to see if we are improving symptoms and then to study their microbiome to see if we can understand how the changes that we're seeing work," said Taylor, who is head of the psychiatry department at the University of Calgary.

That study is just one in a series of Canadian clinical trials aimed at treating a range of diseases with a poop transplant — using an enema or colonoscopy or sometimes with specially formulated pills. It's an idea that wasn't even considered by the medical community just a decade ago.

One Toronto group is transplanting fecal material from lean donors into obese patients to see if the change in gut bacteria prompts improvements in weight and metabolism.

And researchers at Toronto's Princess Margaret Cancer Centre are among the first in the world to give cancer patients a specially selected combination of fecal bacteria harvested from healthy donors to see if that improves the effectiveness of immunotherapy drugs.

The era of the microbiome

Medical science has entered the era of the microbiome.

Scientists all over the world are looking at ways to harness the teeming colonies of creatures living on us and in us to treat disease.

Prof. Kathy McCoy, scientific director of the International Microbiome Centre at the University of Calgary, is researching the effects of the body's gut bacteria on human disease. (University of Calgary)

The surge in research is based on increasing evidence that the body's bacteria could be exerting a profound influence over the mental and physical health of their human hosts.

"We knew that fecal transfers from an anxious, stressed or depressed mouse to a normal mouse would make it anxious, stressed or depressed. But we're now starting to unravel in the microbes how they actually do it," said Brett Finlay, microbiome researcher at the University of British Columbia and co-author of Whole-Body Microbiome.

Using germ-free mice that have never been exposed to microbes, scientists have been able to trigger disease symptoms by transplanting fecal material from affected animals and humans.

There has also been a series of studies revealing differences in the gut bacteria between healthy people and people with Parkinson's disease, Alzheimer's disease, autism, depression and a variety of intestinal disorders.

One of the big questions is whether gut bacteria cause disease or whether disease triggers changes in the gut microbiome.

"What's the chicken and what's the egg?" said Kathy McCoy, scientific director of the International Microbiome Centre at the University of Calgary. "Nobody knows from those association studies what is causation or what is association."

The 'gut-brain axis'

Scientists do agree on one astonishing fact — the gut-brain axis is real, and somehow gut bacteria exert an influence on the brain. How that happens and whether it's possible to manipulate that system to treat disease are unknown.

A group of researchers at Queen's University is launching a clinical trial giving people with depression a powdered formulation of probiotic bacteria to see if changing the gut bacteria will improve their symptoms.

"One of the main mechanisms that we're going to be studying is how the immune system might be mediating the communication between the brain and the gastrointestinal tract," said Caroline Wallace, who is running the clinical trial.

One body, many microbiomes

The science becomes even more complex as researchers move beyond the gut and start exploring the other microbiomes in the body.

"You have a microbiome in your skin, you have a microbiome in your lung, you have a microbiome in your mouth, and they're all different because it's a different environment," said McCoy.

"One place that's controversial at the moment is if there are microbes in the uterus."

And what about in the brain? Many scientists think that's unlikely, but there have been some intriguing observations.

Get ready for gut-health hype

As the research enthusiasm grows, scientists know they could be creating unrealistic expectations.

"You're seeing this stuff being marketed almost ahead of the science," said Timothy Caulfield, a University of Alberta professor who is studying the marketing of unproven microbiome treatments. He said the gut-health hype has already started.

"Unfortunately, once these kinds of ideas take hold, and we've seen that with other technologies like stem cells and genetics, it's often very difficult to remove them from public consciousness."

Prof. Brett Finlay researches the human microbiome at the University of British Columbia. His new book Whole-Body Microbiome reviews the latest discoveries in microbiome science. (Brett Finlay)

As he wrote about the latest science for his new book, Finlay was aware of pressure to include microbiome advice.

"The publisher kept pushing, 'Can't we say this, can't we cure all these things with this?' and I said, 'No there's no data.' I had to keep pushing back," said Finlay. "We're not there yet."

"It's complex but it's also exciting, because we can't change our genes. But we do have the power and probably the opportunity to change our microbiome," said McCoy.

"People are doing this themselves, to themselves, at home. Home fecal transplants, which I wouldn't recommend," said Taylor.

"This might not be the answer, but we owe it to our patients to say we looked at this in a rigorous scientific way."

There is one fecal therapy being routinely used on patients. Fecal transplants have become an accepted treatment for recurring infections of the superbug C. difficile, almost always resulting in a cure.

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