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Not all poop is equally valuable, at least when it comes to fecal transplants. Some people, it appears, generate waste that is better at alleviating conditions associated with gut microbiome imbalances than others, according to a review article published yesterday (January 21) in Frontiers in Cellular and Infection Microbiology.

“Strategies to find super-donors whose stool is especially effective as a curative are still in their infancy, although progress on this topic—or making synthetic super-donors from the stool of many people—could greatly improve application of [faecal transplants],” Rob Knight, a microbiology researcher at the University of California, San Diego, who wasn’t involved in the review, tells The Guardian. 

The authors of the paper looked at studies on the use of fecal microbiota transplants (FMT) to treat Clostridium difficile infection, inflammatory bowel disease, constipation, allergic colitis, and other conditions. They write in their conclusion that the existence of super-donors is “not yet robustly supported by empirical evidence,” but that there is some support for the phenomenon for conditions other than C. difficile infection. “[T]he efficacy of FMT likely depends on the ability of the donor to provide the necessary taxa capable of restoring metabolic deficits in recipients that are contributing toward disease,” the authors write. “Further characterization of super-donors will likely result in the development of more refined FMT formulations to help standardize therapy and reduce variability in patient response.”

The review follows another study on fecal transplants published earlier this month (January 15), in which researchers tested the therapy for ulcerative colitis. Of subjects who received three transplants over seven days from donors, 32 percent were in remission eight weeks later, compared with just 9 percent of patients who received control treatments with their own stool, the authors report. 

Coauthor Sam Costello of the Queen Elizabeth Hospital in Adelaide, Australia, says in a statement that an important difference between this and previous studies was that the stool samples were processed anaerobically. “Many gut bacteria die with exposure to oxygen and we know that with anaerobic stool processing a large number of donor bacteria survive so that they can be administered to the patient,” Costello explains. “We believe that this may be the reason that we had a good therapeutic effect with only a small number of treatments.”