About 1,700 years ago, the Chinese physician Ge Hong came up with the idea that one way to treat diarrhea was to give his patients a “yellow soup” made from stool fresh from a healthy donor. It must have worked, because by the 16th century Chinese doctors were making different “yellow soups” and “golden syrups” that could be used to treat various intestinal ailments or food poisoning.
In Europe we also carried out similar practices, but not with people, but with animals. It was the Italian surgeon Girolamo Fabrizi d’Acquapendente (1537-1619) who came up with the idea of transfaunation, which consisted of transfer rumen contents –a part of the ruminant digestive system– from a healthy animal to a sick one.
At the beginning of the 20th century, the Ukrainian scientist Ilya Mechnikov proposed that the intake of lactic acid bacteria from yogurt was beneficial to health and that they could displace harmful bacteria such as Clostridium. These produced toxic substances that promoted aging.
Fecal microbiota transplants are born
In parallel, the idea that there was something in the feces of a healthy carrier that allowed curing some gastrointestinal pathologies was maturing. It was definitively confirmed thanks to the work of the American doctor Ben Eiseman.
In 1958, Eiseman managed to develop a protocol for the use of fecal enemas in order to cure pseudomembranous colitis caused by Clostridioides difficile (formerly known as Clostridium difficile). Fecal microbiota transplants, or FMTs, were born.
These results sparked a growing interest in studying and characterizing the microorganisms that inhabit our intestines, what we know as the intestinal microbiota. Each new advance made us understand that our general state of health depended on the state of that microbial community.
As of 2012, the first biobanks of feces from healthy donors began to appear. And in 2013, the first clinical trial that conclusively demonstrated that FMT worked for the treatment of recurrent C. difficile infections was carried out.
From the first characterization studies of the intestinal microbiota, it was clear that its composition was affected by diet, by the intake of antibiotics and, above all, by the age of the individual. The microbiota of an infant was different from that of an adolescent, which in turn was different from that of an adult, and this, from that of an elderly person.
So more than one researcher considered whether it was age that affected our communities of microorganisms or whether the opposite was the case. And as always, it can be said that what happens is between both hypotheses.
As we age, our physiology changes and with it the intestinal habitat where our microbes are, which produces a change in their populations. But the opposite is also true according to the results of a study carried out on mice and published in the journal Microbiome.
Rejuvenating transplants (in mice)
The researchers carried out stool transplants from elderly mice (24 months old) to young mice (3 months old) and found that the inflammatory processes associated with aging in the nervous system and in the retina were accelerated. These effects were correlated with an increase in the permeability of the intestinal barrier and an activation of the production of inflammatory cytokines.
Unsurprisingly, they also implanted faeces from young mice into old ones. And then they found that the inflammatory phenomena in the brain, retina and intestine decreased.
It is tempting to think that these fecal microbiota transplants are rejuvenating or, at least, slowing down the aging process. But we have to remember that this was done in mice and may not work the same way in humans. Although of course, the possibility is there, and as we have said before, faeces biobanks already exist.
Should we conserve our droppings?
So it is worth asking if it would be feasible to save a stool sample from when we are young and use it later in life to cure possible intestinal infections or even rejuvenate. This possibility is what is described in a review published in the journal Trends in Molecular Medicine.
In addition to age, diet and antibiotic intake influence the composition of the microbiota. That is the main reason why members of industrialized societies have it very differently from non-industrialized ones. What is proposed in that article is that in this way we could return to a state of “pre-industrial or feral microbiota”.
In a certain sense, it would be something similar to saving the blood of the umbilical cord of the newborn to use it in case of future health problems. Although it must be said that it is much easier to preserve microorganisms from feces than blood.
And what would be the use of performing an autologous stool transplant? Well, apart from treating possible C. difficile infections or even rejuvenating, the authors also propose that it could be used to treat various autoimmune disorders a from obesity.
The idea is feasible, although it is also worth mentioning that evolution has endowed us with our own reserve of microbiota. It seems that the function of our intestinal appendix is to function as a reservoir of healthy microorganisms in the event that we have to recover from an intestinal disorder.
Basically, I think it boils down to applying a maxim of microbiology: if we take care of our microbes, they will take care of us. So eat healthy, because then your microbes will be healthy.
This article was originally published on The Conversation.