Have you ever noticed your stomach balloon up soon after eating a meal? Does that bloated feeling never seem to go away? You’re not alone. For many people, persistent abdominal distention and discomfort can be a frustrating mystery. After undergoing endoscopic procedures, CT scans, and ultrasounds, those struggling with persistent bloating are often met with a shrug, resigned to using Gas-X for relief. One of the most overlooked causes of these symptoms is a condition called SIBO, or small intestinal bacterial overgrowth.
SIBO occurs when bacteria – or, in some cases, microbes called archaea – overgrow in the small intestine. Moving from the stomach to the small intestine and then into the large intestine (or colon), the quantity of bacteria increases. Part of the reason for this is the small intestine has a built-in cleaning mechanism called the migrating motor complex (MMC), which removes waste, debris, and bacteria every 90–120 minutes. Our colon, on the other hand, is both slower moving and less acidic than our stomach and small bowel, which makes it more hospitable for microbes to thrive and multiply.
Much of our microbiome is composed of commensal bacteria — organisms that reside within us without causing harm — that help support our overall health. Beneficial bacteria in the colon ferment food into short-chain fatty acids, which support bowel regularity, the integrity of our gut lining, and even our mental health and immune system. When bacteria begin fermenting food within the small intestine, this produces more gas, which leads to bloating and a host of other digestive symptoms that can feel overwhelming. The small intestine, substantially shorter than the colon, is unable to accommodate nearly as much gas. These eager microbes also have access to fermentable molecules, such as simple sugars and starches, which further increases the overall gas load.
Without a doubt, the number one symptom of SIBO is bloating. Not just mild fullness, but a tight, distended, sometimes painful expansion of your belly – often at its worst later in the day or after meals. You may even wake up feeling relatively normal, only to slowly “inflate” as the day progresses. Bloating in SIBO can be extreme, even painful, and it often doesn’t correlate with how much you’ve eaten.
Along with bloating, many people notice changes in their bowel habits, though this is where the symptoms of SIBO can differ for each person. There are three variants of SIBO, named in accordance with which specific gas is created in excess: hydrogen, hydrogen sulfide, or methane. Each type of gas has unique effects on intestinal motility. The hydrogen-predominant subtypes lead to loose stools, whereas excess methane (known as intestinal methanogen overgrowth, or IMO) tends to cause constipation. A few people experience both, swinging from one extreme to the other. Passing gas, abdominal pain, and even nausea or early fullness are also common.
Every case of SIBO has a backstory, though it rarely appears out of nowhere. One of the most critical aspects of evaluating for SIBO is assessing one’s risk of developing it. For instance, the MMC often stops working properly in SIBO, allowing bacterial overgrowth to take hold in the small intestine. Long-term use of narcotics can slow down gut motility, giving bacteria time to settle in. Prior abdominal surgeries, especially those that lead to scar tissue or adhesions, are another red flag. These adhesions can twist or slow down parts of the small bowel, creating pockets where bacteria can overgrow. Another risk factor that is often overlooked is mast cell activation syndrome (MCAS). This immune condition can cause inflammation and disrupt normal motility, making the gut sluggish and prone to overgrowth. Other risk factors for SIBO include poorly controlled diabetes or a connective tissue disorder, both of which impair the small bowel’s ability to move bacteria through to the colon.
Before arriving at a diagnosis of SIBO, it’s also essential to evaluate for other conditions that cause similar bowel symptoms. Bloating can be caused by many conditions, the most common of which is chronic constipation. When stool remains in the colon for too long, it can ferment. This additional gas load, combined with retained waste, creates an uncomfortable sensation of bloating. Other possible culprits include lactose intolerance, which can cause bloating and loose stools after consuming dairy. A diet high in FODMAPs – fermentable carbohydrates found in certain fruits, vegetables, grains, and dairy – can also mimic SIBO symptoms. Then there are less common conditions, such as congenital sucrase-isomaltase deficiency (CSID), where the body can’t break down certain sugars, and fructose malabsorption, which affects how the gut handles fruit sugars. All of these can resemble SIBO but have different origins requiring different treatments, so it’s essential to obtain the correct diagnosis.
If you have SIBO risk factors and have eliminated other potential causes for bloating, the first step for diagnosis is a breath test. This non-invasive test involves drinking a sugary solution – either lactulose or glucose – and then breathing into a series of tubes over 2-3 hours. The test assesses for those three gases (hydrogen, hydrogen sulfide, and methane) in your breath; because the gases are only produced by bacteria and not by human cells, they can move easily from the small bowel into your bloodstream and on to your lungs to be detected in the air you breathe out. If gas levels rise quickly after you drink the sugar solution, it suggests there’s an overgrowth in your small intestine.
Standard of care for SIBO includes antibiotics that exert their effect in the intestines as opposed to the entire body. These are often referred to as eubiotics because they work by rebalancing the gut microbiome rather than completely replacing it. Rifaximin is the most used option, especially for hydrogen types of SIBO, while neomycin is often added if methane is present. There are also herbal regimens that can treat SIBO, although the data is more limited. Dietary approaches can help, too: the elemental diet is a short-term liquid diet composed of easily absorbed nutrients that starve the bacteria while keeping the body nourished. It’s effective, but it takes commitment (usually two to three weeks) to see it through.
Regardless of the treatment path chosen, the most important thing to address is the underlying cause. SIBO has a notoriously high relapse rate, so unless we’re able to get to the root of what’s making your gut sluggish – whether that’s a cause of slow motility or an underlying condition like MCAS – the bacterial overgrowth will likely come back.
If you’re constantly bloated and wondering what’s going on, you’re not making it up. SIBO is a real condition that affects many people, but the good news is that it’s manageable. With the proper testing and a tailored treatment plan, it’s possible to calm your gut and reclaim your daily rhythm.
