While they may sound totally disgusting, fecal transplants are emerging as a promising treatment for a variety of gastrointestinal diseases, in particular infection with the bacteria Clostridium difficile. They don’t quite involve directly inserting the feces of one person into another, but rather the donor stool is rinsed and strained and then introduced into the recipient, either through an enema or endoscopy, or orally in pill form. The idea is to replace healthy bacteria in the gut after the normal balance is disturbed, for example by antibiotics.

One woman suffering recurrent C. difficile infection was recently successfully treated with this procedure, but interestingly, she also rapidly went from normal weight to becoming obese after receiving the transplant. While the weight gain could be due to a variety of factors, the donor was also overweight, and the recipient had never struggled with her weight before. Researchers are therefore speculating whether something in the transplant could have played a role in her weight gain, and have described the intriguing case in Open Forum Infectious Diseases.

The individual described in the report was a 32-year-old female who presented with recurrent C. difficile infection. This bacterium commonly affects those treated with antibiotics and can cause a variety of unpleasant symptoms, ranging from diarrhea and abdominal cramps to life-threatening complications such as severe bowel swelling.

Alongside testing positive for this particular bacterium, examination revealed that she was also infected with another species called Helicobacter pylori, a common bacterium that can also cause similar symptoms to C. difficile infection. The woman was therefore prescribed a cocktail of antibiotics, but her symptoms recurred after she completed the course. She was then put on different antibiotics, but the same thing happened again. The woman therefore decided to give fecal transplant a go, electing her daughter as the donor.

At the time, the woman was a healthy 136 pounds with a normal BMI of 26. Her daughter weighed 140 pounds at the time, with a BMI of 26.6, but became overweight shortly afterward. Following the therapy, the woman’s symptoms vanished and she no longer experienced recurrent infections.

Sixteen months later, however, the woman reported unintentional weight gain of 34 pounds and met the criteria for obesity. Two and a half years after the transplant, the woman weighed 177 pounds with a BMI of 34.5, despite a medically supervised liquid protein diet and exercise program.

“We’re questioning whether there was something in the fecal transplant, whether some of those ‘good’ bacteria we transferred may have an impact on her metabolism in a negative way,” case report author Colleen Kelly said in a statement.

This would not be the first time that an association between gut bacteria and weight has been reported. Several animal studies have shown that fecal transplant from an obese mouse into a normal-weight mouse can cause a significant increase in fat. However, there are also several other possible factors which could explain her weight gain, for example an increase in appetite following resolution of the infection. Furthermore, links between H. pylori treatment and weight gain have also previously been demonstrated. But given the fact that both the daughter and the mother gained weight, the researchers conclude that the transplant was at least partly responsible for the obesity.

[Via Open Forum Infectious Diseases and IDSA]