Alex Honnold’s gut has way more Prevotella than the average American’s.
Alex Honnold’s gut has way more Prevotella than the average American’s. (Dave Lauridsen)

The High-Performance Secrets Inside Athletes’ Guts

In the name of citizen science, we peered inside the bellies of Outside staff—and seven elite athletes

Alex Honnold’s gut has way more Prevotella than the average American’s.

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It seems like every day, a new study claims to show how your microbiome influences the way your body converts food into energy, responds to illness, or handles inflammation. But as scientists are learning, our bugs are also affected by the way we treat them. The miles you log, the food you eat, the mountains you climb—everything seems to shape your internal ecology, too.

It makes sense, then, that microbiologists are jockeying to get a look at the bacteria inside the stomachs of some of the world’s healthiest, fittest people. How do pro ath­letes compare with amateurs? Do skiers’ guts look different than climbers’? And is there some mythical bug that all kick-ass athletes share? We don’t know—yet.

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“I’ll be the first to admit I eat a decent amount of ice cream,” says obstacle-course racer Amelia Boone. “Definitely more than I should.” The microbes in our digestive systems can affect everything from our mental health to our weight and vulnerability to disease. So why not athletic performance? New science is set to revolutionize the way we eat, train, and live.

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So, in the spirit of science, 15 weekend warriors at Outside contributed samples to the American Gut Project. We also corralled some extraordinary athletes and convinced them to pack fecal swabs off to the lab. Project manager Embriette Hyde and her team then compared our microbiomes with those of student athletes at UC San Diego, a cohort of surfers around the world, and all 10,000 AGP contributors. Crushingly, the Outside microbiomes were nothing to write home about. The elite athletes’? That’s where things got interesting.

Meet the Microbes

The most common bugs in our athletes’ guts

Bacteroides (red): A genus in the Bacteroidetes phylum made up mostly of beneficial bugs that help the immune system keep out dangerous pathogens.

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Prevotella (blue): Another genus in the Bacteroid­etes phylum. Some research has noted high levels in endurance athletes. The most common driver for a gut full of Prevotella is a vegetarian diet.

Lachnospiraceae (orange): Members of this family in the Firmicutes phylum produce butyric acid—a healthy short-chain fatty acid that protects against leaky gut and other conditions.

Faecalibacterium (green): A Firmicutes genus that breaks down fiber into butyrates that aid the immune system. Lower than normal levels have been linked to diseases like Crohn’s and diabetes.

Roseburia (light green): Another genus in the Firmicutes phylum that turns fiber into butyric acid.

Acinetobacter (light blue): A little-studied genus in the Proteobacteria phylum that’s found widely in soil. Scientists don’t know much about its role, but on the off chance it gets into your bloodstream, some of its members are antibiotic-resistant pathogens.

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Ruminococcaceae (purple): Some in this family of Firmicutes are experts at turning resistant starches into beneficial short-chain fatty acids.

Bacillus (yellow): An understudied Firmi­cutes bug that in mice has been shown to protect against pathogens.

Clostridium (pink): Famous for C. botu­linum and C. difficile, most of the bugs in this genus are harmless and help keep the whole bacteria population stable.

Other (gray): Thousands of additional strains of bacteria.

How We Stack Up

The key to making sense of a micro-biome analysis is to look for weirdness.

In general, the more diverse things are, the better. Most contributors to the American Gut Project, including Outside’s staff members, have relatively homogeneous guts. Two big phyla, Bacteroidetes and Firmi­cutes, dominate our gut flora. For many Amer­icans, having significantly more Firmicutes than Bacteroidetes may indicate a higher-fat Western diet, and in some cases obesity. The reverse ratio often points to a more plant-based diet and a leaner physique. That doesn’t always hold true for our pro athletes, however. All seven of them have ­microbiomes that vary considerably from the average American’s. More excitingly, Hyde says, those who compete in similar sports have similar gut bacteria. This suggests that certain factors—such as performing high levels of cardiovascular exercise or spending large amounts of time in the ocean—may affect the makeup of our microbiomes dramatically.

Alex Honnold

Climber, age 32

Home: 2016 Ram ProMaster van
Diet: “I’m probably 95 percent vege­tarian, and full-on vegan 50 per­cent of the time. I eat a fuckload of fiber, mostly a plant-based diet of roughage.”
Gut biome: Bacteroidetes dominant
Takeaway: Honnold’s gut has way more Prevotella than the average American’s. Some research has connected high levels of this genus to intense exercise, but Hyde thinks the bug—which turns complex carbs into energy—likely thrives because of his vegetarian diet.

Climber Emily Harrington
Climber Emily Harrington (Dave Lauridsen)

Emily Harrington

Climber and mountaineer, age 31

Home: Squaw Valley, California
Diet: “I try to eat paleo. No bread, minimal carbs and sugar, and lots of vegetables, fruit, and fat from coconut, avocados, and nuts.”
Gut biome: Firmicutes dominant
Takeaway: Harrington’s gut has high levels of Clostridium, a tricky genus that contains both frightful pathogens and helpful strains that keep the gut running smoothly. In addition, she and mountaineer Adrian Ballinger, who live and train together, have similar bugs—an indication of how much your environment can affect your gut.

Mountaineer Adrian Ballinger
Mountaineer Adrian Ballinger (Dave Lauridsen)

Adrian Ballinger

Mountaineer, age 41

Home: Squaw Valley, California
Diet: “Emily and I eat mostly the same stuff. I probably eat more meat than she does. We both drink coffee every day and have maybe a glass or two of red wine each night.”
Gut biome: Firmicutes dominant
Takeaway: In addition to having Clostridium levels that are similar to his girlfriend, Ballinger’s microbiome is loaded with Roseburia and Faecalibacterium. Both produce butyrates, which reduce inflammation.

Ultrarunner Rob Krar
Ultrarunner Rob Krar (Dave Lauridsen)

Rob Krar

Ultrarunner, age 41

Home: Flagstaff, Arizona
Diet: “Very loosely I would describe it as greens and grains based—healthy eating while not denying myself the pleasures of a beer in the evening and desserts. I eat very little meat but do consume eggs, milk products, and fish.”
Gut biome: Bacteroidetes dominant
Takeaway: Krar has more Bacillus than any other elite athlete sampled—a bacteria that barely registers in most folks. Not much is known about Bacillus, but mice studies have shown that it protects against pathogens.

“I’ll be the first to admit I eat a decent amount of ice cream,” says Boone. “Definitely more than I should.”
“I’ll be the first to admit I eat a decent amount of ice cream,” says Boone. “Definitely more than I should.” (Dave Lauridsen)

Amelia Boone

Obstacle-course racer, age 34

Home: San Jose, California
Diet: “It’s pretty normal—the standard focus on quality proteins, fats, and carbs—but I’m not super regimented. I’ll be the first to admit that I eat a decent amount of ice cream. Definitely more than I should.”
Gut biome: Bacteroidetes dominant
Takeaway: Boone’s gut is home to signif­icantly more Acinetobacter than the American Gut Project usually sees. It’s commonly found in dirt—something that Boone, a Tough Mudder veteran, spends a lot of time rolling around in.

Skier Cody Townsend
Skier Cody Townsend (Peggy Sirota)

Cody Townsend

Skier, age 34

Home: Tahoe City, California
Diet: “It’s light on grains, because I’m allergic to gluten. I look for whole foods. I can’t just be on a trip and think, I’m hungry—oh, there’s a hot dog. I have to plan ahead and go for nuts, fruit, and vegetables. It shifts my entire diet.”
Gut biome: Bacteroidetes dominant
Takeaway: Townsend’s gut has almost four times more Parabacteroides than anyone else surveyed. Parabacteroides are great at turning plant fibers into energy and often bloom in folks who consume a lot of resistant starch—like oats, cold potatoes, and cold rice—which bugs don’t feast upon until it hits the colon.

Surfer Fergal Smith
Surfer Fergal Smith (Mats Kahlstrom)

Fergal Smith

Surfer, age 30

Home: Lahinch, Ireland
Diet: “I would say it’s fairly good. I mostly just eat the vegetables I grow. And I only drink spring water.”
Gut biome: Bacteroidetes dominant
Takeaway: Smith, who lives on an organic farm, has the kind of gut that ­microbiologists lust after. Loaded with high levels of anti-inflammatory Bifidobacterium and Ruminococcaceae, plus lots of Prevotella, it reflects his vegetable-based diet and has the diversity you’d expect from a person connected to both land and sea.