Could Your Old Poop Cure You of Future Diseases?

The thought of transplanting another person’s poop into your colon may sound unpleasant, and understandably so. Feces are a smelly mixture of water, undigested food, dead and living bacteria, and other cells and substances. However, the live bacteria in feces have proven their worth in treating diseases and ailments of the digestive tract. This is why doctors have been transferring feces from healthy donors to sick patients for years—usually by colonoscopy, enema, or pill—to restore gut health.

The concept is relatively simple: Good bacteria from donated feces will colonize the patient’s gut if the recipient’s microbiome is out of balance and will outcompete any trouble-causing bacteria. For example, healthy fecal bacteria can be used to treat an infection with Clostridioides difficile bacteria, which can infect the human colon and cause mild to life-threatening diarrhea. In clinical trials, fecal microbiota transplants are estimated to be more than 90 percent effective at clearing C. diff infections. And just last month, researchers in Norway wrote in the journal Gastroenterology that patients with irritable bowel syndrome (IBS) suffer less from bloating, stomach cramps, and constipation after being treated with a fecal transplant—even three years after receiving it.

David Ong, a gastroenterologist at Mount Elizabeth Hospital in Singapore, sees even greater potential for these treatments, as gut microbes interact with our brain and other organs. Ong, who in 2014 was the first doctor in Singapore to perform a fecal transplant on a patient infected with C. diff, says recent studies suggest the intervention could also help people with inflammatory bowel disease or obesity, or those on the autism spectrum with gut problems related to picky eating. There are currently more than 100 clinical trials investigating the effect of fecal transplants on conditions ranging from depression to epilepsy and Covid-19 to cancer.

“Genes are what you’re born with, and it is what it is,” says Ong. “But the gut microbiome is something that you can manipulate. And if you can manipulate it to a good outcome in terms of disease, that’s excellent.”

There’s just the small matter of finding the right poop, though. In addition to working as a gastroenterologist, Ong cofounded the startup Amili, which has collected more than 1,000 stool samples for transplants over the past three years. However, most willing donors are excluded after filling out questionnaires and having their stool, blood, and saliva tested in the lab.

Lifestyle, diet, medical history—including the use of antibiotics, which can kill off gut bacteria—and how someone was born can all rule people out. (Newborns delivered through the vagina pick up their first gut bacteria from their mother as they move through the vaginal canal and show greater microbial diversity than those delivered by C-section.) In the Norwegian trial, the stool samples used to treat 87 patients with IBS came from one donor: A 36-year-old man who was born vaginally; breastfed; was a nonsmoker; had been treated with antibiotics only a few times; exercised regularly; and consumed high amounts of protein, fiber, minerals, and vitamins. Generally, once a donor is deemed healthy enough, lab technicians will examine their stool sample. The technicians are looking for diverse microbiomes and, in particular, bacteria known to compete with harmful bacteria.