Some people with lactose intolerance think they don’t fart much after eating dairy, but a new device that measures hydrogen metabolised by gut microbes says that’s not the case, reports The Scientist.
Anyone with lactose intolerance knows that just one mouthful of ice-cream usually results in some uncomfortable gut sensations and stinky side effects about 30 minutes to a couple of hours later.
People with lactose intolerance cannot break down lactose, the natural sugar in dairy products. When gut microbes encounter this unabsorbed lactose, they ferment it and release hydrogen gas, which exits the body as flatulence.
While most people with lactose intolerance find that they expel flatulence more after eating food with dairy, not all of them report doing so. Breath analysis is one way to measure hydrogen gas produced by gut microbes, but researchers can’t use it for continuous monitoring.
Currently, there is no way to objectively measure continuous gas production in the gut for lactose intolerance or any other digestive condition, limiting what researchers can learn about the connection between gut metabolism and these symptoms.
However, Brantley Hall, a gut microbiome researcher at the University of Maryland, and his team, have designed a new device to change that.
Using a “Smart Underwear” gas sensor that attaches to the inside of underwear, they found that people with lactose intolerance fart much more than they think.
The findings, which the team reported at the recent Digestive Week 2026 meeting in Chicago, present new insight into how people perceive their own flatulence and a continuous method to monitor gut metabolism, which could help scientists better understand gastrointestinal conditions like irritable bowel syndrome (IBS).
“We have spent years learning which microbes live in the gut and what genes they carry but actually measuring what those microbes are doing in real time, in a living person going about their day, has remained out of reach,” Hall said.
“Hydrogen gas is one of the most direct readouts of microbial fermentation activity, and we realised that if we could measure it continuously and non-invasively, we would have a window into gut microbial metabolism that nobody had before.”
To find out how often people actually fart after eating lactose, Hall and his team enrolled 37 generally healthy participants without IBS symptoms in a four-day, randomised crossover study. Participants consumed 20g of lactose or 20g of sucrose and then wore Smart Underwear for the next eight hours.
They repeated the process the day after, but ate the opposite sugar. Smart Underwear work by continuously monitoring for farts while also collecting data on temperature, humidity, and movement.
The researchers found that of the 37 participants, 24 were likely to be lactose intolerant due to their elevated microbiome activity on the day they ate lactose compared to sucrose. To the team’s surprise, of the 24 people with presumed lactose intolerance, only 12 out of the 24 reported that they farted more after eating lactose.
But the Smart Underwear told a different story – 22 out of the 24 people actually farted more.
“People aren’t reliable narrators about their flatulence patterns,” Hall said. What he found most intriguing about these results was that “gas production and gas perception are not the same thing, and our data suggest the gap between them is larger and more common than most of us assumed”.
“That has real implications for how we design studies and interpret symptom-based outcomes.”
Hall hopes that Smart Underwear can help researchers and clinicians better understand what normal gas production in the gut looks like and how it might change due to various diseases. He’s eager to collaborate with other teams to conduct more studies that would benefit from continuous gas monitoring of the gut microbiome.
“This is the beginning, not the end,” he said.
The Scientist article – Smart Underwear Tracks Farts in Real Time (Open access)
See more from MedicalBrief archives:
UK study casts doubt on widespread lactose intolerance diagnoses
Windy barrister wins thousands of pounds in flatulence case
Food fad? New illness? Trying to find what is really behind gluten sensitivity