What is a fecal microbial transplant? - Kathryn M. Stephenson and David L. Suskind

1,700 years ago, a Chinese alchemist named Ge Hong was renowned for his special soup that could cure diarrhea-stricken patients. The stew was deep yellow and had an intense aroma. And, like many family recipes, it had a secret ingredient. But in this case, that ingredient didn’t come from the kitchen—it came from the bathroom.

It might seem unwise to consume feces, and today, there aren’t many doctors who would prescribe Ge Hong’s recipe. However, exciting new research suggests that taking poop into the body in other ways might benefit our health. One such treatment is fecal microbial transplantation, and the secret to how it works lives in your gut.

Trillions and trillions of bacteria, viruses, fungi, and archaea consider your bowels their home. Collectively, these microbes make up what’s known as your gut microbiome, and each of these organisms possesses dynamic, specialized abilities that seem to be essential for human life. They break down our food, make vitamins, train our immune system and circadian rhythm, and even protect us from infections. In return, they receive a nice warm place to live, complete with an all-you-can-eat buffet.

Some research suggests our microbiomes might start forming in the womb, but if not, they certainly get started when we're born. During a vaginal birth, infants take in some of their mother’s fecal matter and microbe-filled fluids. From then on, our microbiomes are constantly diversifying with exposure to various foods and environments. This is essential for maintaining gut health. If poor nutrition, chronic disease, or antibiotics disturb this delicate balance, the body can become vulnerable to problems like bacteria and fungal overgrowth or infectious diarrhea.

But infusing a new batch of microorganisms into the intestine seems to help reset the gut microbiome—this is where fecal microbial transplants come into play. This line of treatment is still very new, and there are tons of unanswered questions about how it works. So currently, the US Food and Drug Administration only allows doctors to use fecal transplants experimentally for battling one of the toughest gut infections—antibiotic-resistant Clostridiodes difficile.

This infectious bacterium forms spores in the colon that are immune to antibiotics and very difficult to destroy. Patients dealing with this infection can experience months of intermittent fevers alongside bouts of abdominal cramping and extreme diarrhea despite antibiotic treatment. So when symptoms get this bad, it’s time for a fecal microbial transplant.

To start the process, a gastroenterologist first retrieves some feces, typically from a stool bank. These frozen samples are particularly impressive number twos—the selected donors go through a strict process to ensure their samples are infection-free. In fact, these protective protocols are so stringent that one prominent stool bank’s acceptance rate is less than 3%.

Next, the gastroenterologist gets that sample inside the patient via a pill or, more commonly, a tube into the stomach or colon. Finally, the transplanted microbes migrate through the tract until they find the colon, where they quickly multiply and displace the infectious invader. This process is so effective that it cures over 80% of patients in just one treatment.

Because each stool sample is unique, the FDA still classifies fecal transplants as an experimental treatment rather than a formal medication. But promising research in rodents suggests new ways we might use fecal bacteriotherapy in the future. For example, fecal transplants from non-diabetic mice improved insulin resistance in mice with type 2 diabetes.

Similarly, some studies have shown mice exhibiting anxiety and depression become calmer after transplants from their less anxious peers. Scientists studying humans have even started finding different microbial patterns associated with various intestinal, autoimmune, oncologic, and even psychiatric disorders. So, it seems entirely possible that altering a patient’s microbiome could allow for multiple new modes of treatment.

We still have a lot to learn about what makes the “best” gut microbiome, or the most beneficial fecal transplants. But for now, at least we can say that our feces have a bright future.