As technology improves, scientists are discovering just how important our gut microbes can be. The tiny organisms in our digestive tracts have an astounding amount of influence over the rest of our bodies. Consequently, we have a lot of incentive to keep our guts happy and healthy. One up-and-coming treatment is the fecal transplant, which is exactly what it sounds like: the transfer of stool from one organism into the gastrointestinal tract of another

Proponents of the treatment say it works by adding healthy bacteria to a sick person’s gut. That’s true, say researchers, but it’s also adding a lot of other things. They published their report on the subject in the journal PLOS Biology.

The concept of a fecal transplant is still pretty new. When the researchers searched existing science literature for studies that mention fecal transplants, here’s what they found:

Next, the team dug through dozens of papers to find out exactly what our poop is made of. They found that, on average, studies have shown that human feces is about 25 percent water and 75 percent solid material. As predicted, a lot of that solid matter—between 25 and 54 percent—is made of bacteria. But that still leaves almost half of the poop’s contents unaccounted for.

The rest, the researchers say, is a pretty big mishmash. There are colonocytes, or cells from the lining of the intestine; single-celled microorganisms called archaea; viruses; fungi; protists; and small molecules called metabolites, which are involved in metabolic processes.

“Individual components of fecal matter can yield health benefits and may work synergistically to restore homeostasis,” the authors write. “There is a cautious need for continued reductionism to understand the precise benefit and interactions of various fecal components.”

In other words, it’s possible that healthy bacteria may not be the only driving force behind a fecal transplant’s curative powers.

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