A medical illustration shows a germ called Clostridium difficile, which can be eliminated from the body through a fecal transplant. (Lois S. Wiggs, Janice Carr/AP/Centers for Disease Control and Prevention)

To be a professional cyclist, one must have guts, microbiologist Lauren Peterson says, and she doesn’t just mean that in the metaphorical sense. Peterson, herself a pro endurance mountain biker, has theorized that elite cyclists have a certain microbiome living in their intestines that may allow them to perform better, and if you don’t have it, well, there may soon be a way to get it. . . .

“Call it poop doping if you must,” Peterson told Bicycling magazine last week about her research.

Peterson, a research scientist at the Jackson Laboratory for Genomic Medicine in Farmington, Conn., heads up an initiative called the Athlete Microbiome Project, in which she compares stool samples of elite cyclists to amateur bikers. Her findings, she said, which had her compare stool samples from 35 participants, according to the Scientist magazine, shine a light on a handful of microorganisms that apparently separate the guts of elite athletes from average people.

The most important, perhaps, is Prevotella. Not typically found in American and European gut microbiomes, Prevotella is thought to play a role in enhancing muscle recovery.

“In my sampling, only half of cyclists have Prevotella, but top racers always have it,” she told Bicycling. “It’s not even in 10 percent of non-athletes.”

Not everyone’s convinced, however, that just hosting a certain set of microorganisms in one’s gut will enhance athletic performance.

“The fact that the microbiomes [in elite athletes and average people] are different is interesting, but it doesn’t mean they caused any athletic performance benefits,” microbiologist Jonathan Eisen, who teaches the subject at University of California Davis, told The Post on Wednesday.

But along with her unpublished data, Peterson cites a controversial reason to believe the gut’s contents may affect performance — her own “poop doping.”

Peterson hosts Prevotella in her gut, thanks to a fecal transplant she administered herself three years ago. Her donor? Another elite athlete.

Peterson said she didn’t decide on the potentially dangerous fecal transplant to enhance her performance during her mountain bike races; she did so in an attempt to treat a host of symptoms that have affected her since she was a child and contracted Lyme disease.

“I had no microbes to help me break down food, and I had picked up bugs in the lab where I was working because my system was so weak and susceptible,” she told Bicycling.

But, she continued, “I couldn’t find a doctor who could help me” since in the United States, fecal transplants are only performed to treat serious cases of Clostridium difficile, a disease that causes chronic diarrhea. And so Peterson went rogue.

Peterson detailed her decision to perform the risky procedure the podcast “Nourish Balance Thrive” last year. She admitted to thinking it was a “bad idea” at first because if not done with proper screenings of both parties, it could worsen a person’s problems or even present new health challenges. But through chance, she came across a donor, an elite long-distance racer, who had his microbiome mapped and screened after a case of food poisoning, which showed he was otherwise healthy. So Peterson took antibiotics to wipe out her own gut bacteria and essentially performed a reverse enema.

“I just did it at home,” she said of the February 2014 procedure. “It’s not fun, but it’s pretty basic.”

Within a month, Peterson said, she began feeling better than she’d felt in years. She said before her transplant she was having trouble just training on her bike; just months later, she said she began winning pro races.

Of course, there is no way to prove the fecal transplant, opposed to other changes she may have made in her lifestyle or even the placebo effect, was the cause for her rebound.

Eisen, the UC-Davis professor, went further, calling it “irresponsible” to attribute Peterson’s newfound energy to the procedure.

“There is no way to show without a clinical study that [the fecal transplant] changed her performance,” he said. “When you do a medical study, the best way to do it is when you’re blind [i.e., the patients don’t know what treatment they’re getting].”

Without that, he said, “It’s just not appropriate to make any conclusion.”

Peterson, who has not yet published her findings, appears to agree it’s too early to make any concrete conclusions about how the microbiome affects performance, but she’s convinced her research could lead to new types of performance aids should her theories bear out.

“What we’re learning is going to change a lot for cyclists as well as the rest of the population,” Petersen told Bicycling magazine. “If you get tested and you’re missing something, maybe in three years you’ll be able to get it through a pill instead of a fecal transplant. We’ve got data that no one has ever seen before, and we’re learning a lot. And I think I can say with confidence that bacterial doping . . . is coming soon.”

Eisen, however, said he hopes athletes pump the brakes before trying any type of “bacterial doping” on their own.

“Fecal transplants have real risks,” he said, noting if a donor isn’t properly screened, the procedure could insert possibly deadly pathogens into another’s system.

He added even if Peterson’s research does bear out and if an athlete can find a healthy donor, he’s “skeptical” about whether the procedure would work for everybody, as each individual’s gut is uniquely different, not only in contents, but in operation.

“In general, it seems more likely that if you wanted to optimize someone’s microbiome for athletic perform, it’s going to have to be a personalized optimization,” he said. “I think there’s potential for manipulation of the microbiome to impact athletics performance, but we’re a long ways away.”

Peterson did not return The Post’s request to comment further at the time of publication.

This story has been updated.