The case of a normal-weight woman who rapidly became obese after receiving a fecal transplant from an overweight relative has raised new concern over the screening of donated stool.
The patient, who underwent the novel procedure to treat a recurring bacterial infection in her intestines, has gained more than 40 pounds since the transplant and continues to gain weight, according to a case report published Wednesday in the journal Open Forum Infectious Diseases.
The patient has been unable to shed the unwanted weight through diet or exercise, according to her doctors.
"This case serves as a note of caution when considering the use of non-ideal donors for fecal microbiota transplant (FMT), and we recommend selecting non-overweight donors," wrote the paper's authors, Dr. Neha Alang, an internist at Rhode Island's Newport Hospital; and Dr. Colleen Kelly, a gastroenterologist at the Warren Alpert Medical School of Brown University.
It remains unclear exactly what caused the dramatic weight gain. However, the physicians note that studies conducted on mice show that lean mice can become fatter if they receive fecal microbes from overweight mice.
"We're questioning whether there was something in the fecal transplant, where some of those 'good' bacteria we transferred may have had an impact on her metabolism in a negative way," Kelly said in a prepared statement.
Viewed for many years as a fringe medical treatment with a high "snicker factor," fecal transplants have recently shown promise in fighting Clostridium difficile infections.
So called C. diff infections cause swelling of the intestines, diarrhea and abdominal pain. They often occur when the microbes that naturally inhabit the gut are killed by antibiotics and invading C. difficile bacteria move in and take over.
By collecting stool from a healthy donor and placing it within the intestines of a patient, "good" bacteria are reintroduced to the gut and help to restore microbial order.
In the case of the then-32-year-old Rhode Island patient, doctors treated her C. diff infection with five courses of antibiotics, only to see the infection flare up again after each treatment.
Ultimately, she elected to have a fecal transplant.
"As per the patient's request, her 16-year-old daughter was chosen as the stool donor," the doctors wrote. "At the time of FMT, her daughter's weight was about 140 pounds, but it increased later to 170 pounds."
The patient weighed 136 pounds at the time of the transplant, according to authors, and her infection was cured by the procedure.
However, 16 months later she had gained 34 pounds, raising her body mass index, or BMI, from 26 to 33. "She weighed 170 pounds and had become obese," the doctors wrote. "She has continued to gain weight despite efforts to diet and exercise and at 36 months post-FMT her weight was 177 pounds (BMI 34.5)."
The doctors speculate on a variety of potential causes of the weight gain, including the effects of antibiotic treatment, stress caused by the illness, and the disappearance of the infection.
Yet based on the fact that the woman was not overweight prior to the procedure, as well as the animal studies, the researchers said it was now their policy to use only non-obese donors for FMT.
In an editorial that accompanied the paper, doctors at Massachusetts General Hospital wrote that genetics probably played a role in the woman's weight gain.
However, they said the case underscored the need to carefully vet stool donors on the basis of BMI and other health indicators.
Even though some patients might be more open to receiving stool from a family member, this could lead to a number of complications, the editorial says.
"The published case report raises many questions about the selection of FMT donors," wrote Drs. Ana Weil and Elizabeth Hohmann.
"FMT has not been studied in large-scale controlled trials, and we have much to learn about the effects of this treatment beyond the intended restoration of a diverse microbiota," they wrote.