The prevalence of one particular gut condition remains a big question mark, but what is SIBO exactly? And how do you know if you have it? Keep scrolling for everything you need to know, according to experts.
Dawn Egan’s stomach has been a pain point for her since school. As early as age six, the fashion editor, now 40, remembers not being able to eat much of anything without feeling pangs of discomfort.
Doctor after doctor reassured her that it was “just irritable bowel syndrome (IBS),” that “she’d grow out of” and tossed a slew of solutions her way to stifle the pain and pull her out of a seemingly never-ending cycle of constipation and diarrhea.
She was told to cut out all carbs, then sugar, then dairy; pop Pepto or MiraLax or magnesium. But nothing stuck.
By the time she was a teenager and into her 20s, Egan had a hard time finding anything to eat that didn’t cause her body to “balloon” with gas, the ripples of pain from her puffed-out stomach often leaving her doubled over on the floor.
It wasn’t until 2012, when Egan was 28, that a naturopathic doctor told her matter-of-factly that she had small intestinal bacterial overgrowth, or SIBO.
What is SIBO?
The condition was originally identified as the reason why some people who’d had GI surgery or a digestive disease developed malabsorption (or failed to soak up nutrients from food). The result of their misshapen or malfunctioning gut was “a kind of stagnant lake, where bacteria could proliferate [in the small intestine],” says Eamonn M. Quigley, MD, director of the Underwood Center for Digestive Health at Houston Methodist Hospital.
This bloom of bugs ate up nutrients that the person would have otherwise digested, triggering deficiencies and symptoms like diarrhoea and fatigue.
But as scientists use new technology to measure bacteria in the gut, and research increasingly explores the many effects of those bugs on our health, the concept of SIBO has been applied to a host of other digestive woes—to much controversy.
Researchers agree that SIBO constitutes an excess of bacteria in your small intestine, Dr. Quigley says. When bacteria multiply in excess in your small intestine, they might consume key nutrients from your food before your gut can. (Typically, most of your gut bugs are in your colon, or large intestine, where they feed on the scraps your body can’t digest, like stubborn plant fibres.)
What some experts believe is that these squatting microbes can trigger immediate tummy troubles (not just malabsorption); for instance, research shows that the gasses they release may cause bloating and abdominal pain, while toxic byproducts of their feasting could pull extra fluid into your colon, causing diarrhoea.
Other bacterial activities may spike inflammation and change how your gut muscles function, both of which could mess with your poo. Because these symptoms are also hallmark signs of IBS, some research suggests that in people like Dawn, for instance, SIBO could be the underlying culprit.
Why is SIBO so controversial?
Other experts say the lack of a reliable diagnostic test for SIBO leaves its role in triggering IBS—or any other gut problems—up for debate.
While scientists have identified that certain bugs (like E. coli and Klebsiella) tend to play an outsize role in setting off SIBO symptoms, there’s also a tonne of variation in people’s microbiomes, making it tough to say that any one microbe is always to blame.
It follows that diagnostic standards for SIBO have focused more on quantity than type of bug, with researchers determining that at least 1,000 CFU (colony forming units) of bacteria per millilitre of small intestinal fluid generally points to the condition.
But it’s challenging for health care providers to get that sample and accurately assess how many microbes really populate it (more on that later).
So it’s no wonder the prevalence of SIBO remains a big question mark.
“It ranges from 4% to 50% of people, depending on which research study you read and how the test to make the diagnosis was performed,” notes Brian E. Lacy, MD, PhD, a board-certified gastroenterologist at Mayo Clinic in Jacksonville, Florida, and co-editor in chief of the American Journal of Gastroenterology.
He suspects it’s at the lower end of that range—but given the condition’s vague definition, experts are split between whether SIBO is under- or over-diagnosed. And the disagreement surrounding if, when, and how to treat it often leaves folks like Dawn with more questions than answers.
Various factors can set the scene for bacteria to swarm your small intestine.
Obstructions in your intestines: Normally, after food exits your stomach, it chugs through your intestines in a consistent flow, thanks to rhythmic muscular contractions. But anything that interferes with this process or obstructs the path can leave particles lingering along that route, including in your small intestine—where opportunistic bacteria can nosh on them and multiply.
Surgeries: As noted above, this can occur with structural abnormalities in your GI tract caused by, for example, surgeries that leave behind scar tissue or diseases that affect the shape of your bowels (like diverticulosis, which creates pouches in the intestinal walls).
Small tumour or Crohn's disease: A partial blockage from a small tumour or a narrowing of the intestines from the inflammation caused by Crohn’s disease can also slow the flow of food in the small bowel and lead to bacterial buildup, explains Mark Pimentel, MD, a board-certified gastroenterologist at Cedars-Sinai in Los Angeles and the director of the Medically Associated Science and Technology (MAST) programme.
Autoimmune conditions: More broadly speaking, any condition that reduces the movement (or “motility”) of your gut can set the stage for SIBO, Dr. Pimentel says. This includes autoimmune conditions like scleroderma and type 1 diabetes, as they can damage the nerves that control the impulses for these muscle movements.
Food poisoning: Some research shows that bacterial infections linked with food poisoning (spurred by bugs like Salmonella or Campylobacter) could injure those nerves too. The possible emergence of SIBO in the wake of this gut slowdown could be why more than 10% of people who get a stomach infection experience lingering GI symptoms, Dr. Pimentel says, which is often called post-infectious IBS.
Too little stomach acid: Having less than a typical amount of stomach acid can also let more of the bacteria you eat make their way to your small intestine, Dr. Lacy says. That can happen if you naturally secrete too little acid (a.k.a. hypochlorhydria, which can occur with age or be caused by an infection or stomach inflammation) or if you consistently take proton pump inhibitors (medications that reduce your stomach acid, like Prilosec, Nexium, or Prevacid) over a long period of time.
Figuring out if you have SIBO and whether it’s causing your GI issues is tricky—and subjective.
For folks like Dawn who have been dismissed for years, getting a new diagnosis can feel validating. Again, IBS isn’t often traced to a specific cause; what’s worse, research suggesting that it may be the result of a disconnect between your brain and your gut is often misinterpreted to mean it’s “all in your head.”
SIBO, on the other hand, can feel more tangible, if only because it can be shown on a test. But the reality is, there is still quite a bit of subjectivity in both identifying SIBO and effectively treating it.
First, there’s the challenge of getting to your small intestine, which is smack-dab in the middle of your GI tract. “It’s relatively inaccessible compared to collecting faecal or saliva samples,” Dr. Quigley says.
In the past, doctors leaned on a procedure called small bowel aspiration to diagnose SIBO, which involves passing a tube through a patient’s mouth and into their intestines (like an endoscopy) to extract fluid, and then sending that off to a lab to be assessed for bacteria.
Aside from being invasive, costly, and risky, this is not as precise as it sounds; a 2021 study by Dr. Lacy found that these samples are often contaminated by bacteria in the mouth.
Today, most SIBO diagnoses come by way of a breath test—which is safer, cheaper, and can even be done at home. You simply drink a sugary beverage and then blow into a tube at various intervals for a few hours, which measures levels of hydrogen, hydrogen sulfide, and/or methane gas in your breath.
As Dr. Pimentel explains, these substances are produced by bacteria (hydrogen and hydrogen sulfide) or archaea (methane) when they consume carbs and are not created by human cells; so if you’re puffing out any of these gasses shortly after you’ve eaten sugar, that’s a strong indicator of excess microbes in your upper bowel, where they don’t belong.
In a person without SIBO, the sugar won’t get fermented (and the gas produced) until it hits the normal colony of bugs in their colon, which takes longer.
But a few things can make breath tests imprecise. For one, the sugary substances used, typically lactulose or glucose, might move through some peoples’ guts faster than others, Dr. Quigley says, so some of the gas you’re exhaling could be due to normal fermentation by bacteria located down in your colon, resulting in a false positive.
There’s also the possibility that you absorb most of the glucose as it passes through the first part of your small intestine. This means that a big bloom of microbes farther along your GI tract don’t get to ferment it, so neither of the gasses is created, and you wind up with a false negative, Dr. Lacy says.
Interpreting the results can also be complicated. There’s subjectivity in how a doctor reads any given test; some physicians add hydrogen and methane breath levels together, which could give you a false positive, Dr. Lacy says.
Others might point out higher versus lower levels around those cutoffs as more “severe” or “borderline” results, as has been the case for Dawn, who has done multiple breath tests in the last decade.
(And it’s unclear whether more gas directly equates to worse symptoms.) “I’ve found that every doctor’s version of what’s okay and what’s not is vastly different,” Dawn says.
In the absence of a gold standard SIBO diagnostic, doctors still broadly disagree on how big of a role the condition may play in triggering the whole IBS milieu.
That said, a boom of research is uncovering more information about what constitutes a healthy gut microbiome—not just in terms of the types of bacteria present, but also what they’re doing and producing, Dr. Quigley says.
And the more we learn, the more clearly we’ll be able to determine when and for whom SIBO could be to blame for ongoing gut troubles.
Identifying and treating the root cause of SIBO is challenging
Treatment tends to be a journey for folks diagnosed with SIBO—which might come as a surprise for a condition that hinges on extra bacterial buggers. An antibiotic to knock out the overgrowth should do the trick, right?
Not so fast. The first challenge is determining which bacteria you’re dealing with. You’ll remember from above that experts haven’t nailed down the most problematic species, and a breath test does not reveal the specific ones at play if SIBO is found.
So health care providers are “taking an educated guess when they prescribe [an antibiotic],” Dr. Lacy says.
rifaximin (Xifaxan) is often considered the best bet because it isn’t systemically absorbed (meaning it stays in your gut), and doesn’t seem to wreck your microbiome. Indeed, recent research suggests rifaximin is generally effective for treating SIBO. But that doesn’t mean taking it is always a breeze.
For law student Kate Collins-Palmer, who was diagnosed with SIBO via a breath test in 2015, rifaximin seemed to make things worse, at least temporarily.
She’d been dealing with consistent bloating, gas, and abdominal pain, as well as severe fatigue, but within a couple days of starting the antibiotic, “I felt like the life was being sucked out of me,” she says, describing a kind of tiredness that immobilized her on the couch. (Fatigue, dizziness, and muscle spasms are among the potential side effects of the drug, though it’s worth noting that serious ones occur in fewer than 1% of folks who take it.) Because she couldn’t finish the two-week course, she wasn’t able to test its efficacy.
But for those who experience fewer or less debilitating side effects, the longer-term relief can be well worth it.
As was the case for product designer Madeline Warshaw, who says that after taking rifaximin in 2022, she felt the “closest” she had to “normal digestion” since before her bouts of unpredictable diarrhoea began in college several years prior; she also experienced a “huge increase” in her concentration ability.
The above research suggests the drug can clear SIBO in as many as 70% of cases—though it’s still not FDA-approved for this use.
Madeline’s experience demonstrates another big challenge with treating SIBO: Tamping down bacterial overgrowth doesn’t necessarily prevent it from coming back, because it’s not treating the underlying cause, Dr. Lacy says.
Indeed, 45% of people who take an antibiotic course for SIBO experience a recurrence of their symptoms. And it’s not generally recommended to keep taking antibiotics repeatedly because of the risk of breeding antibiotic-resistant bugs, Dr. Quigley says.
The key, then, is to address whatever may be predisposing you to that bacterial boom in the first place. And to figure that out, your doctor might order additional tests, like an endoscopy, enteroscopy, or colonoscopy (to look inside your stomach, small intestine, or colon, respectively).
If they find a physical obstruction or blockage, they may be able to remove it. But if your doctor suspects an underlying condition is weakening or limiting the contractions in your gut, you may need to consider a medication that can help promote motility, Dr. Pimentel says.
Adjusting your diet may also help to keep excess bacteria at bay (though no diet has been definitively proven to resolve SIBO).
In the early stages of a flare-up and for a temporary period of time, limiting carbohydrates can reduce the amount of fuel you’re offering to the hungry microbes. Dawn’s doctor, for instance, suggested that she cut out most grains, dairy, starches, and sugars.
A low-FODMAP diet, typically recommended for those with IBS, is sometimes suggested for people with SIBO too, as it eliminates a particular group of tough-to-digest carbs (found in dairy, wheat, beans, and some fruits and vegetables) that bacteria can otherwise feast on. (If you’re planning on following this plan—or any other restrictive diet—it’s important to work with a doctor or registered dietitian to avoid nutritional deficiencies.)
In keeping with the advice of an integrative gastroenterologist, Kate also took the approach of nixing most dairy, gluten, and sugar from her diet. Within a couple of months, she felt some relief from her gut symptoms as well as more energy and less brain fog.
The tricky thing is, her diet, like all the others above, wasn’t sustainable long-term; in fact, some research shows that sticking to a low-FODMAP diet for an extended period of time, in particular, could shift the balance of your microbiome in a negative direction by starving your good gut bugs.
Hence why people with SIBO can wind up yo-yoing between diets, as Dawn has. She’ll cut things out only to be told to reintroduce them, “but I don’t know how, or how much to try, or when to eat” to avoid symptoms for the long haul, she says.
While research on the nuances of SIBO is moving us closer to answers and more effective treatment options, in the meantime, it’s easy for people like Kate to feel “defeated by your intestines,” she says.
She still experiences bloating, gas, and belly pain on occasion, but she’s found a semblance of balance by making dietary tweaks when she needs them. It’s a kind of resignation, or body détente, that will be familiar to others who live with a chronic disease—particularly one with so many unknowns.
A version of this article originally appeared on Self.
