What is a fecal transplant and what is it used for?

Fecal transplantation, or more accurately, fecal microbiota transplantation (FMT), is the administration of fecal matter from a healthy donor to a recipient, with the aim of restoring or modifying their fecal microbiota (FM). FMT is performed by administering the processed product from the feces of one or more donors into the recipient's gastrointestinal tract via colonoscopy , enemas, jejunal catheter, or capsule ingestion.

The human microbiota is the set of microorganisms that coexist and develop on the various surfaces (skin and mucous membranes) of our bodies. It is estimated to be composed of approximately 100 trillion bacteria, viruses, and fungi . This means that, together, they are more abundant than human cells and account for between half a kilogram and a kilogram of the weight of a normal adult. Of all the parts of our body, the gastrointestinal tract is the main reservoir of microorganisms and has been considered one of the most complex ecosystems on Earth. Our microbiota has been compared to a new, still virtually unknown organ that houses approximately 150 times more genes than the entire human genome.

A healthy gut microbiota can be defined by the presence of groups of microorganisms that enhance the host's metabolism, confer resistance to infections, inflammatory processes, the development of neoplasia or autoimmunity , promote endocrine functions, or collaborate with neurological function through the so-called gut-brain axis. In this context, which affects a part of medicine that was unknown until recently, one of the surprises that the microbiota has given us is that its administration from a healthy person to another with certain diseases can contribute to their total or partial cure.

This fecal microbiota transplant could actually only be considered a transplant in its own right if we consider the components of the microbiota to be an integral part of the "donor" organism, which is debatable. In fact, at the beginning of this therapy , neither the Council of Europe nor the European Commission considered it as such, nor did state agencies such as the ONT address it. The situation changed recently when the European Union decided to bring together in a single regulation ( Regulation (EU) 2024/1938 of the European Parliament and of the Council of 13 June) "all substances of human origin intended for humanuse " ( Substances of Human Origin ,SoHO ). This regulation, in addition to the cells and tissues for transplantation, includes elements as diverse as blood and its derivatives, breast milk, hair, and microbiota. This means that all of these would become the responsibility of agencies similar to the ONT in the 27 EU countries, albeit with greater powers.

Interestingly, the concept implicit in FMT is not new . In the field of veterinary medicine, the usefulness of the ingestion of cattle feces to relieve certain intestinal ailments has been known since the 17th century. Similarly, the Bedouins advised soldiers during World War II to ingest dromedary feces to treat dysentery . In Chinese medicine, fecal suspensions were successfully used to treat poisoned patients or those with severe diarrhea, and very different types of digestive processes were treated with various fecal preparations .

At present, FMT is clearly indicated only for Clostridioides difficile infection, a germ responsible for severe diarrhea, which carries a mortality rate of 4-7% and which in 20% of cases is recurrent and difficult to control with antibiotic treatment. The results achieved in these situations are reasonably good, but in any case it is necessary to be aware that it is a complex treatment , which needs to be applied by experienced teams and that it is not free of side effects . Its extrapolation to other conditions in which its use is being evaluated, still in the experimental phase, such as ulcerative colitis or Crohn's disease , should be viewed with hope, but not without caution until its usefulness is established.

In a recent document signed by theNational Transplant Organization (ONT) and the Spanish Agency for Medicines and Medical Devices (AEMPS), the entire process of fecal donation, its altruistic nature, the handling, preparation, and administration of microbiota preparations , all with the high quality and safety standards required by these regulations, are described in detail in accordance with European SoHO regulations. This demonstrates that, although the preparation of fecal extracts and their subsequent administration seems simple and within anyone's reach, the truth is that it is a relatively complex procedure if performed correctly and should in no way be trivialized.

In short, although the topic may suggest the occasional scatological joke, fecal microbiota transplantation is already gaining ground in the treatment of some diseases and raises hopes for many others . It is, therefore, a technique with a promising future in various digestive processes, but progress must be made with full scientific guarantees so that these expectations are not dashed.