Scientists testing if poop transplants could help obese people lose weight — and keep it off

The transplants will be done by infusing stool into the large bowel of the obese patients via colonoscopy

Sharon Kirkey 4 minute read October 3, 2016

Dr. Kenneth Croitoru, a clinician-scientist at Mount Sinai’s Zane Cohen Centre for Digestive Diseases

If you could lose weight by letting a doctor inject a skinny person’s poop into your intestine, would you consider it?

As the science linking gut bacteria with a litany of human diseases explodes, University of Toronto researchers are exploring human-to-human stool transplants to combat obesity.

The team has just completed the first phase of a $1.5 million, federally funded project that might ultimately offer obese people an alternative to costly, risky and radical gut-reconfiguring weight loss surgery.
Studies suggest people with obesity have different intestinal bacteria than those who don’t. Scientists believe different microorganisms living in the gut play a key role by acting on hormones that affect insulin sensitivity and the amount of calories absorbed from food.

The Toronto study comes on the heels of several animal studies showing that when germ-free mice — mice raised in ultra-sterile environments and free of intestinal bugs — are fed stool from obese mice, or obese humans, the animals put on more weight and body fat than those fed bacteria from the guts of lean mice or skinny humans.

As well, recent studies suggest bariatric surgery not only works by making it physically harder for people to overeat by reducing the size of the stomach, but also by altering the gut’s microbiome. It may explain why, soon after surgery, even before people start to shed weight, their blood-sugar levels improve dramatically.

Donor stool transplants are already proving effective in combatting the hospital-acquired superbug C. difficile, while the “avant garde” — albeit rather icky — therapy is also being tested against ulcerative colitis and Crohn’s disease.

In a new study published Monday in the journal Nature Genetics that involved more than 1,500 healthy people, Toronto researchers identified four key genetic markers that appear to be associated with changes in the gut microbiome — suggesting that genes, and not just diet and environment, influence the makeup of the organisms living in our guts.

“We have to look at these markers, what genes are they reflecting and how is it that a change in that gene has any influence on how gut bacteria occupy the gut,” said lead author Dr. Kenneth Croitoru, a clinician-scientist at Mount Sinai’s Zane Cohen Centre for Digestive Diseases.

The obesity study is part of the University of Toronto Fecal Microbioata Transplantation Outcomes Program, a collaboration currently seeking healthy stool donors, ages 18 to 50, on its website. (“Be a Donor! We would love your poop for a research study.”)

The researchers are mapping changes in fecal bacteria in people before and after bariatric surgery. “We chose the biggest guys — I mean BMI’s of 50,” said Dr. Herbert Gaisano, a gastroenterologist and researcher at Toronto Western Hospital, who, together with U of T professor Dr. Johane Allard, is co-principle investigator of the study.

First, researchers took stool from the obese patients before surgery and fed it to germ-free, skinny mice “to see if the mice will either start gaining weight or increase insulin resistance,” Gaisano said.

Stool will then be taken from the same patients three and six months post-op, and given to fat mice in the hope the fat mice won’t gain weight.

Ultimately, if they can learn how surgery alters the type and number of gut bacteria, “then we could potentially deploy (stool transplants) of that specific fecal flora to induce weight loss,” without people having to resort to surgery, Gaisano said.

The team will also explore whether stool taken from lean, healthy volunteers will improve blood sugar control
and weight in “morbidly” obese patients.

People will be randomly assigned to one of two groups: one group will receive stool from a carefully screened donor, the other his or her own stool (the “control group.”) The poop will be infused via colonoscopy into the large bowel.

Despite the promise of fecal transplants, the researchers are cautious. The field is moving so rapidly, “we haven’t learned to walk yet and we’re starting to run,” said Croitoru, who is also participating in the obesity study.

“The idea that there may be a microbiome that confers obesity — and even that isn’t clear if that’s really true in humans, we suspect it might be — can you imagine if you give the wrong bugs and you start to induce obesity or diabetes or any of these other diseases,” he said.

As well, “you’re taking a donor at random and just hoping the donor has the right microbiota based on the fact they’re not obese,” Croitoru said.

“Let’s be clear: This is not the cure to obesity nor is it the only cause of obesity,” he said. “This is just an element of obesity.”


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