Breath carries clues to gut health

Maybe you use an Apple Watch to count your steps or an Oura ring to track your sleep. Or maybe you rely on a glucose monitor to surveil your sugar levels. We’re living in an era with unprecedented access to our health data, thanks to gadgets that keep digital eyes on our beating hearts, movements and blood. This electronic scrutiny can even pull intel from the invisible ­— our breath.

Today, a handful of home-based tests, like the Trio-Smart or the FoodMarble AIRE, let consumers measure gases wafting from each exhalation.

Molecules in the breath can flesh out a picture of health, conveying info from the microbes making homes in our guts, says Ali Rezaie, a gastroenterologist at Cedars-Sinai Medical Center in Los Angeles.

But claims that frequent breath testing can reveal which foods to eat or avoid may be a puff overblown. Rezaie advises caution on using such tests to assess food tolerances. “I don’t think that will give you a clear-cut answer,” he says.

Still, there’s real science behind breath tests, Rezaie says. In clinical settings, they can help doctors detect gastrointestinal disorders. And breath molecules might one day serve as red flags for infections or diseases like asthma.

Microbes produce gasses in our guts

Our guts contain a wonderful world of microbes. Bacteria, archaea and fungi can all can cohabitate in a diverse community of microscopic life — and many even do us some good. They help break down food, shore up our gut barrier and produce compounds used by our bodies, says Andrew Kau, an allergist-immunologist at Washington University in St. Louis. “They have a very wide variety of effects on human health,” he says.

Sometimes, though, those effects can veer harmful. In people with small intestinal bacterial overgrowth, or SIBO, bacteria that typically reside in the colon creep up the intestines to grow where they shouldn’t. “That means there are extra bacteria sitting in your small bowel,” Rezaie says. More bacteria means more microbial digestion of the foods we eat, and that “can produce a lot of gas.”

Doctors can test for SIBO by measuring gases like hydrogen and methane in the breath, but it takes more than a single puff. Before the test, patients need to eat a bland, low-fiber diet, then fast overnight. At the clinic, they’ll blow into a breathalyzer machine that analyzes captured gases. Next, patients consume a sugar solution and blow again every 15 minutes for the next couple of hours.

It’s an involved process doctors have standardized to determine if a patient’s gas levels are out of whack. Getting such tests to work at home can be a little tricky, Rezaie says. The machine his team uses is calibrated twice a day to ensure measurements are correct. That’s why ­— if patients can’t get to an expert — he’s partial to commercial home-based systems where users collect their breath and send it to a lab. Devices that do it all in home may be less accurate.

And though gases like hydrogen and methane can hint at what’s happening in the gut, they’re just the start of what our exhalations can reveal.

Microbial signatures waft on the breath

Every time we exhale, we release hundreds of complex chemicals called volatile organic compounds. Think of them like a perfume, says Audrey John, an infectious disease pediatrician at Children’s Hospital of Philadelphia. If you poured perfume on a table, it would evaporate, scented molecules vanishing into the air.

This year, Kau and John showed that these kinds of molecules can serve as signatures of specific gut microbes. Scientists had speculated that some of the volatile organic compounds sailing on our breaths might come from our microbiomes, but no one knew for sure. It’s a difficult question to answer because volatile organic compounds are everywhere: emitted from our food, off-gassing from our mattresses and released by our body’s own tissues.

Kau’s team found that mice with microbiomes had a different set of volatile organic compounds in their breath than those without. And when the team transplanted microbiomes into the germ-free mice, the animals’ breath compounds changed. They now resembled those emitted by the original microbiome-carrying animals, Kau and John reported in Cell Metabolism. That’s evidence that gut microbes drive the differences seen in these kinds of breath compounds, Kau says.

The researchers wondered if breath compounds could telegraph the presence of gut microbes linked to disease. In a clinical study of 41 children, kids with asthma had different breath compound signatures than kids without the disease, the researchers found. They tied these signatures to the amount of Eubacterium siraeum, a bacterium previously linked to pediatric asthma, in the kids’ stool.

The breathalyzer tech isn’t ready for primetime, John says. That’d require a much larger study to validate the findings. In the meantime, she’s interested in using breath to spot newborn sepsis, a life-threatening condition that can stem from infection. Then, people like John could identify infants at risk and intervene before they get sick. “To me,” she says, “that would be a really profound outcome.”