Whether you are obese or thin might come down to the type of bacteria in your gut. In March researchers will test a new fecal microbiota transplant capsule. (Mark Lennihan/AP)

There’s no denying that America has an obesity problem. According to the Centers for Disease Control and Prevention, more than one-third of all adult Americans are obese. While many of the options to overcome obesity – a more nutritious diet, daily exercise and a less sedentary lifestyle – have been well-documented, there’s potentially a new option that’s pushing the boundaries of innovation: fecal microbiota transplant capsules.

Yes, we’re talking about capsules that contain a tiny amount of human poop.

In March 2016, researchers at Massachusetts General Hospital in Boston will launch a clinical trial (“Fecal Microbiota Transplant for Obesity and Metabolism”) to study the impact of gut bacteria on weight. By transplanting the intestinal bacteria from a stool sample of a healthy, lean person into the gut of a person suffering from obesity, it might be possible to change the gut bacteria population of that obese person. As those “lean microbes” start to populate the obese person’s gut, it could reduce that person’s propensity to obesity.

Or, to put it in less scientific terms, ingesting a tiny amount of fecal matter from a thin person could make you thin, too.

For a period of six weeks, some of the 20 patients taking part in the clinical trial will be given pills containing a tiny amount of a thin person’s fecal matter, while the others will be given a placebo made of powdered cocoa and gelatin. Then, over the next 12 months, the researchers will track the weight and health of the 20 participants to see if there is any difference between those ingesting the poop pills and those ingesting the placebos. Theoretically, the people ingesting the fecal pills should lose more weight than the people ingesting the placebos.

[Here’s what it takes to be the perfect poop donor]

The stool samples for the fecal capsules are similar to those provided by the OpenBiome project, a nonprofit stool bank founded in 2012 by a team of microbiologists, clinicians and public health advocates from Harvard and MIT to expand safe access to fecal microbiota transplantation therapies and catalyze research into the human microbiome. In this study, Massachusetts General Hospital is not working with OpenBiome; instead, the researchers will use their own capsules.

As Zain Kassam, the chief medical officer at OpenBiome, told me in an email conversation, a lot of testing has gone into ensuring that OpenBiome’s stool samples have been optimized to contain just the right types of microbes. “Safety is OpenBiome’s number one priority,” he told me. “In fact, only 2.8 percent of candidate stool donors pass our robust safety protocols. Having graduated from Harvard, I can say it’s harder to be admitted to OpenBiome as a poop donor than to get into Harvard.”

But will the poop capsules really work when it comes to curing obesity?

The lead researcher conducting the clinical trial, Elaine W. Yu, an assistant professor at Harvard Medical School and a clinical researcher at Massachusetts General Hospital, told me that there has been encouraging scientific evidence that intestinal microbes might actually play a role in treating obesity.

“A small study in humans has already been done that demonstrates that altering gut bacteria affects human metabolism,” Yu told me. There’s also evidence, says Yu, that transfer of gut bacteria from lean or obese humans into germ-free mice can determine whether these mice turn out to be lean or obese. In another study, transfer of gut bacteria from mice who have undergone bariatric surgery to non-operated germ-free mice led to weight loss and decrease in body fat.

But on the other hand, we’re still talking about freeze-dried poop pills.

Ingesting the fecal matter of another human being – no matter how glamorously thin – just seems, well, yucky. There’s a reason why we’re told not to swim in water that may have been infected with human fecal matter and why we wash our hands after using the bathroom – it’s all those nasty bacteria and bad microbes your mother warned you about.

Kassam of OpenBiome, though, discounts those fears. First of all, participants in the clinical trial will not include pregnant women, people with significant gastrointestinal disorders or people with significant food allergies – all people who might suffer adverse side effects from ingesting the wrong gut bacteria.

Secondly, the process of screening the stool donors is so rigorous, and that helps to eliminate any chances for infection. As Yu told me, “Our screening process is more rigorous than what blood donors undergo.” Capsule preparation has been reviewed and approved by the FDA, Yu added.

The good news is that fecal transplant techniques have already come a long way, even if they are still in their infancy. In addition to new research and testing, the techniques for delivering the gut bacteria are also becoming more advanced. Until as recently as last October, you would have had to get the beneficial microbes inserted directly into your gut via a colonoscopy or a plastic tube inserted through the nose. Now there are pills.

Certainly, from a consumer perspective, the potential to pick up a bottle of pills or capsules from the local pharmacy sounds more enticing than the prospect of a colonoscopy or a tube containing fecal matter inserted into the nose. Somewhere, a Big Pharma marketing executive must be smiling at the prospect of what might be possible in the future.

“Although it’s too early to tell when the 53-year-old truck driver who has struggled with his weight will be able to pick up FMT capsules at his local pharmacy,” says Kassam, “I can imagine a universe in the not too distant future where a microbial treatment can complement diet and exercise to deeply impact the obesity epidemic.”

What we could be talking about, if the upcoming clinical trial does show a cause and effect relationship between gut bacteria and obesity, is an entirely new way of thinking about the human microbiome. We already know that gut bacteria could play an important role in a number of different health and metabolic processes, so why not obesity?

Kassam is optimistic that researching the relationship between the microbiome and obesity might lead to a new public health paradigm: “Medicine sometimes gets trapped in dogma and embraces the conventional escalator to clinical impact. But sometimes a new, bold path pops up serendipitously, and a few brave optimists take the elevator and change the way we think about medicine.”

The big question is: Can intestinal bacteria really determine whether we are lean or obese? To answer that question, you might just have to trust your gut.

UPDATE: This article has been updated to reflect the fact that Massachusetts General Hospital (MGH) is not working with OpenBiome on this clinical trial. MGH has their own capsules for the project.