Checking up on the health of your gut and its resident microbes is soon to be as easy as swallowing a gas-sniffing capsule no bigger than a vitamin.
Previously trialled in pigs, the capsules — which transmit hydrogen, carbon dioxide and oxygen levels to a receiver as they traverse the digestive system — have successfully passed phase-one human trials.
The "exciting homegrown" invention shows most promise for patients suffering irritable bowel syndrome (IBS), according to Adelaide gastroenterologist Dan Worthley.
"Even though IBS is the most common gastroenterological problem, there's no laboratory diagnostic test for it," he said.
The swallowable capsule, published today in Nature Electronics, might one day not only help diagnose IBS, but also track whether treatments work and let clinicians give feedback to patients.
"I think psychologically it could be a really valuable tool for managing patients," said Dr Worthley, who also runs a gastrointestinal biology lab at the South Australian Health and Medical Research Institute.
Bacteria: tiny gas pumps
Like it or not, there's always gas in your digestive tract: your stomach, small intestine and large intestine.
A little is swallowed air, and some is produced through chemical reactions, but the lion's share is generated by your gut microbiome: the trillions of microbes that call your gut home.
They do this by fermenting undigested food for energy and, in the process, churn out gases, such as hydrogen.
While having some gas in our gut is beneficial, too much fermenting bacteria, particularly in the small intestine, can lead to bloating and severe pain.
This "small intestine bacteria overgrowth" is thought to be a driving factor in IBS.
Scoping out how much gas is in the gut and where it's produced can give doctors an idea of what's going on in there, but that's easier said than done.
Clinicians use breath tests to calculate gut hydrogen levels. Gas in the digestive system is absorbed into the blood and carried to the lungs, where it's exhaled.
(That's right — as you're reading this, you're breathing out hydrogen produced in your intestine.)
But these breath tests aren't great, said RMIT materials scientist and study-co-author Kyle Berean.
"They have an accuracy of less than 70 per cent for many diagnostic procedures," he said. "It's pretty much a toss of coin."
And even if a breath test returns high hydrogen levels, they can't say where in the metres of intestines a bacterial overgrowth might be located.
Eight years in the making
In 2010, Kourosh Kalantar-zadeh, a materials scientist at RMIT, was approached by a gastroenterologist to develop a better breath test.
Given the inherent problems with breath tests, Professor Kalantar-zadeh could not help. But then he thought: what if he put the breath test inside the gut?
In the years since, he and colleagues developed swallowable capsules that monitor temperature and a range of gases.
Finally, last year, it was time to try them in healthy people. Trials were conducted with a Monash University team led by gastroenterologist Peter Gibson.
The capsules are around the size of a fish oil tablet or vitamin.
Trial participant Keegan Hughes said it felt "a little odd" when he swallowed the capsule.
"It's strange to think there's a machine in me, but it went down really easily."
The membrane at one end of the capsule case allowed gas to enter, but not liquid.
A microcontroller let the researchers put the capsule in idle mode between measurements to prolong battery life.
A transmitter sent information to pocket-sized receivers every few minutes which, in turn, pinged it via Bluetooth to a smartphone.
And when the temperature readout dropped below 35 degrees Celsius, the subjects knew their capsule had made its way out.
The results of the trial illustrate just how important fibre is to keep your digestive system moving.
One participant swallowed the capsule after a high-fibre diet. The capsule was excreted after 21 hours.
He then swallowed another capsule after eating very little fibre.
Four days passed, but the capsule didn't. It wallowed in his large intestine until he ate some fibre. The capsule finally reappeared 36 hours later.
How quickly food passes through the gut and what people eat shape microbiome populations, said Carly Rosewarne, a microbiologist at the CSIRO in Adelaide.
Pills that measure how quickly food winds its way through the gut are already available, but they can't sense gases at the same time.
"That's where these [new] sensors are really quite powerful," Dr Rosewarne said. "They can tell you how fast or slow the gut is moving and how much gas is being produced in response to what someone has eaten."
Next-generation ingestible capsules
The next generation of gas-sniffing capsules could be designed to sense hydrogen sulfide — also known as rotten egg gas.
Not only does it make your farts stink, it's a key factor in inflammatory bowel disorder.
In the meantime, the researchers must raise funds for phase-two trials, Dr Berean said, before they bring the product to market.
"Our aim is to get it in patients' hands quickly.
"I've had gastrointestinal issues. It makes me want to get it out there more."