Skip to main content
phys ed

The question: I suffer from depression and I’ve been reading lately that microbes in the gut can affect your mental health. If I take a probiotic supplement that changes my gut microbes, will that make me feel better?

The answer: The medical community has long known that the trillions of microbes that inhabit the human gut perform many essential jobs. The microbes, made up mostly of “good” bacteria – collectively called the microbiota – help digest food, promote the normal development of the immune system and act as vanguards against potentially harmful germs.

And now a growing body of research suggests that what’s happening in the gut may also have an impact on the brain.

In a study published in February, for instance, Belgian scientists reported that two types of gut bacteria tend to be depleted in people with depression. The significance of this study is still open to debate. Although the scientists found “an association” between the absence of certain gut microbes and depression, they didn’t actually prove one thing causes the other, says Dr. Mark Sinyor, a psychiatrist at Sunnybrook Health Sciences Centre in Toronto.

Even so, the results are intriguing and add support to earlier studies that demonstrated mood and behaviour could be altered by manipulating the gut’s microbial contents. Some of this groundbreaking research – done in lab mice and small groups of patients – was performed at the Farncombe Family Digestive Health Research Institute at McMaster University in Hamilton by Dr. Stephen Collins and Dr. Premysl Bercik.

In one experiment, the researchers “induced anxiety-like behaviour in mice” by colonizing them with bacteria from human patients with high levels of anxiety, says Collins, director of the Institute.

In another experiment, the introduction of a very specific strain of bacteria into the guts of 22 patients with irritable bowel syndrome produced beneficial results. Their bowel irritation temporarily lessened. What’s more, the patients, who also suffered from depression, reported an improvement in their mood.

Collins says that the bacteria used in his study somehow modified the body’s immune system, which in turn triggered a positive response in brain cells. It’s also possible that gut microbes may produce compounds that directly or indirectly affect the brain. But figuring out exactly what’s going on isn’t easy because depression itself is a complicated condition.

It was once thought that depression resulted from a “chemical imbalance” in the brain. Based on this theory, patients should feel better by simply taking medications that restore the brain’s correct chemical balance.

But now researchers believe that there may be many different causes of depression, which is characterized by both structural and activity changes in the brain. Some evidence also suggests inflammation may play a role.

“There are probably multiple types of depression that all masquerade as a single entity,” Sinyor explains. “And that’s the reason why we have many treatments that work, but certain treatments work for some people while other treatments work for others.”

Both Collins and Sinyor think it’s possible that research may eventually lead to new bacterial-based treatments for depression and other mental-health disorders. But such therapies may help only some patients.

Collins notes that the composition of gut bacteria can be modified – at least temporarily – in a variety of ways, including changes in diet, taking certain medications (such as antibiotics) and physical activity. “But sooner or later, in most instances, it will revert back to where it was before.”

The types of bacteria that inhabit the gut tend to vary from person to person. “Your genetic makeup plays a role in determining what kind of bacteria are going to find your body a suitable place to live,” Collins says.

That means it may be extremely difficult to alter an individual’s gut bacteria in a sustainable way. Despite these obstacles, some companies are already vigorously marketing their supplements, which contain an assortment of bacterial strains, as remedies for mental-health problems.

“I have seen ads that state a probiotic will calm nerves and help mood,” Collins says. “This is jumping the gun,” he says, adding that such claims usually aren’t supported by the existing research.

He also points out that the specific bacterial strains used in his research studies are not yet commercially available.

Collins is concerned the public may develop unrealistic expectations with the release of more and more studies exploring the gut-brain connection. Indeed, numerous research teams are now doing fecal transplants (or bacterial transfers) for mental-health disorders ranging from autism to Alzheimer’s disease. Although this research seems promising, it’s far too soon to be recommending probiotic supplements for any particular condition.

“It’s unfortunate how the public can be led to believe in something without there being a great deal of evidence,” Collins says.

Paul Taylor is a patient navigation adviser at Sunnybrook Health Sciences Centre. He is a former health editor of The Globe and Mail. Find him on Twitter@epaultaylor and online at Sunnybrook’s Your Health Matters.

Live your best. We have a daily Life & Arts newsletter, providing you with our latest stories on health, travel, food and culture. Sign up today.