Fecal transplants are being used as treatment for individuals with Clostridium difficile infections, but it appears that concerns of the Food and Drug Administration (FDA) over its safety are not unwarranted.

A woman who had fecal microbiota transplant (FMT) to treat her recurring superbug infection has rapidly and unexpectedly gained weight after the procedure. Her donor, who was her own teenage daughter, was notably overweight.

The case, which was described in the journal Open Forum Infectious Diseases on Wednesday, Feb. 4, has prompted doctors to consider the effects of gut bacteria on metabolism and health.

In 2011, the then 32-year-old woman who weighed 136 pounds and had a BMI of 26 received donor stools from her healthy but overweight teenage daughter. The procedure was made in order to restore a healthy balance of the mother's gut bacteria and cure her C. diff. infection.

Although the fecal transplant was successful, the woman's weight significantly increased 16 months after the procedure. She has gained a number of pounds since she had the transplant and continued to gain weight.

"The patient actually said this: 'From the moment I had the fecal transplant, I felt like a switch flipped in my body," said Colleen Kelly from the Warren Alpert Medical School of Brown University. "She felt like prior to the fecal transplant, she had never had to worry about weight."

Over this short period, the woman became medically obese. By this time, she weighed 170 pounds and had a BMI of 33. Her doctors also said that, despite having a medically supervised diet and exercise, she was not able to shed unwanted weight. Three years after the treatment, the unnamed woman weighed 177 pounds and had a BMI of 34.5.

Although there are other potential factors that could have contributed to the woman's weight gain, such as genetic factors, antibiotics used, aging and stress, the woman never had weight problems before. Interestingly, earlier studies involving animals have found a link between bacteria in the gastrointestinal tract and extra weight.

Researchers of these studies have found that transferring gut bacteria from obese mice to those with normal weight leads to fat increase. They also recommended opting for stool donors without weight problems for fecal transplant. The authors of the new study also suggested the same.

"With the occurrence of weight gain after FMT in this case, it is now our policy to use nonobese donors for FMT," the researchers wrote. "This case serves as a note of caution when considering the use of nonideal donors for FMT, and we recommend selecting non-overweight donors for FMT."

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