SIBO (small intestinal bacterial overgrowth) is an imbalance of the microorganisms in your gut that maintain healthy digestion. When too many bacteria, or the wrong kind, populate the small intestine, it can lead to uncomfortable symptoms such as gas and diarrhea. It can also inhibit your ability to digest and absorb nutrients from food.
SIBO stands for “small intestinal bacterial overgrowth”. It means that the bacteria that live in your small intestine are overgrown and the things that normally maintain balance among your gut flora aren’t working. It’s normal and healthy to have bacteria living in your small intestine, but too many can cause problems with your digestion — especially if they're the wrong kind. The wrong bacteria can overwhelm the beneficial bacteria that you need to be there, and they can upset your digestive system by feeding on products that aren’t meant for them.
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Your body maintains the balance of flora in your gut through a complex network of chemical and mechanical functions. For SIBO to occur, one or more of these functions must be failing. Gastric acid, bile, enzymes and immunoglobulins are some of the chemicals that control bacteria in the small intestine. Different conditions can inhibit these chemical functions. The emptying of food contents from the small intestine into the large intestine is another important cleansing mechanism. If this mechanism is slowed or impaired, the bacteria in the small intestine have more time to breed, and the bacteria in the large intestine may begin to creep upward.
Bacteria in the small intestine digest carbohydrates and convert them into gas and short-chain fatty acids. More bacteria can mean more gas and other byproducts, which often triggers diarrhea. The bacteria also consume proteins and vitamin B12 meant for us, and bile salts that are supposed to be there to help you digest fats. All of this leads to poor digestion of fats and poor absorption of nutrients, especially calcium and fat-soluble vitamins. The result is a variety of gastrointestinal symptoms in the short term, and malnutrition in the longer term. Over time, vitamin and mineral deficiencies can cause lasting damage to your bones and nervous system.
Some studies indicate that up to 80% of people with irritable bowel syndrome (IBS) have SIBO. The prevalence among healthy people is unknown. Doctors assume that SIBO is generally underdiagnosed. Mild cases may be asymptomatic, while moderate cases feature many non-specific symptoms that overlap with other conditions, such as IBS. SIBO isn’t often directly tested for, and even when it is, the tests available are imperfect.
SIBO symptoms can resemble a variety of other gastrointestinal conditions, and often another condition has contributed to SIBO. You may experience some or many of these, depending on the severity of your condition:
Low stomach acid (hypochlorhydria) reduces the body’s ability to moderate bacterial growth. Factors that may reduce your stomach acid levels include:
Small intestine dysmotility means that waste is retained for too long in the small intestine before emptying into the large intestine. This allows the small intestine bacteria to continue to multiply, while the large intestine bacteria may make their way into the small intestine. Some dysmotility disorders include:
Structural problems in the small intestine can inhibit motility and the regular clearing of residual bacteria and create extra nooks and crannies for bacteria to accumulate. These can be caused by gastrointestinal diseases or by complications of surgery. Structural problems include:
Overuse of certain medications can upset the normal balance of flora. These include:
Advanced age is associated with lower stomach acid and motility levels as well as higher levels of medications that might encourage SIBO.
Medical interventions such as abdominal surgery and radiation exposure can cause structural problems in the small intestine as well as damage the mucosal lining, which affects your immunity.
Immunodeficiency disorders can affect your intestinal immunity to certain bacteria.
Certain gastrointestinal conditions can affect intestinal motility or create intestinal structural problems, including:
While foods aren’t the original cause of SIBO, certain foods do encourage the overgrowth of the wrong bacteria in the small intestine. If you’re feeding them their favorite foods, they're going to grow more, and that will trigger more of your SIBO symptoms. By the same token, you can help reduce the overgrowth by starving the problematic bacteria of their favorite foods. This strategy has led to a number of proposed SIBO diet plans. The diets vary, and so do individual results. But in general, they tend to recommend limiting carbohydrates. These include:
SIBO and IBS share many symptoms, and you can have both. The main difference is that bacterial overgrowth can be clinically verified and treated. IBS, on the other hand, is a functional disorder that is diagnosed when your symptoms can’t be clinically explained.
When you seek a medical diagnosis for your symptoms, you’ll probably be tested for SIBO as well as other comparable conditions, such as lactose intolerance. If you test positive, you can be treated for those conditions, and hopefully, your symptoms will go away.
If they don’t all go away, you may have another condition. If no discernable cause can be found, that’s when you’ll be diagnosed with IBS. Sometimes, IBS is found to be a contributing cause of SIBO.
The symptoms of SIBO overlap with many other gastrointestinal conditions, some of which you may already have. So when you seek a medical diagnosis, SIBO might not be the first thing your healthcare provider suspects. If, however, your symptoms and medical history suggest SIBO, your healthcare provider may suggest a breath test to verify it. This simple, non-invasive test measures hydrogen and/or methane levels in your breath to determine the presence of gas-producing bacteria in your gut. If your levels are above a certain number, it suggests an abundance of bacteria.
Your healthcare provider may suggest additional tests to look for signs of causes and complications of SIBO, including:
Common symptoms of SIBO, including gas and bloating, abdominal pain and distension are uncomfortable enough. But left unmanaged, SIBO can cause more serious complications with long-term consequences. Malabsorption of fats, proteins and carbohydrates can lead to malnutrition and vitamin deficiencies. In particular, vitamin B12 deficiency can cause nervous system problems and anemia. Poor calcium absorption can lead to long-term osteoporosis or kidney stones.
SIBO is often a complication of another condition, and often causes complications of its own. When treating SIBO, healthcare providers need to address:
A course of antibiotics is the standard medical treatment for bacterial overgrowth. Healthcare providers will then seek to manage your most acute complications. This might mean nutritional support and supplementation for vitamin and mineral deficiencies. It might mean a strict short-term diet to manage symptoms and then a modified longer-term diet plan to replenish your nutrition and keep bacterial overgrowth in check.
Ultimately, healthcare providers will want to locate and treat the underlying cause of your SIBO. This may require additional testing. If they suspect you have a motility disorder, they might prescribe motility agents to help stimulate the process and keep things moving. If they identify a structural problem, they might recommend surgery to correct it.
It’s not uncommon for SIBO symptoms to return several months after you've finished a course of antibiotics, especially if you have an underlying condition that predisposes to SIBO. Antibiotics are an acute treatment, but not a long-term solution. It’s important to try and address the underlying cause of your SIBO. Sometimes that’s a separate medical condition that can be more actively managed. Sometimes it’s a structural problem that can be addressed in surgery. You might need to adjust your existing medications or alcohol use to keep bacteria growth under control.
If you can’t identify or fix the underlying cause, you can try to manage bacterial overgrowth with a low-carb diet and probiotics. Studies on these solutions are inconclusive, but anecdotal evidence suggests they may help. Especially as you're nearing the end of your antibiotics, try to avoid overfeeding your bacteria with carbohydrates for a few weeks. Try to install some new beneficial bacteria to balance the harmful ones by taking probiotics daily.
To induce remission of SIBO, some healthcare providers recommend a short-term elimination diet. That means restricting all carbohydrates from your diet temporarily to starve the bacteria. The more severe version of this would be the elemental diet, a liquid diet of pre-digested formulas. The elemental diet gives your gut bacteria nothing to digest while providing all the nutrition you need. It’s only prescribed for short-term, therapeutic purposes. SIBO is one of them.
A variety of other low-carb diet plans may work as an at-home elimination diet or maintenance diet. You may follow these short-term and then gradually add different foods back in, observing how your system responds. Or you may find that you thrive by sticking to a diet long-term. There are many kinds of low-carb diets and many of them claim to help with SIBO. We recommend the Specific Carbohydrate Diet (SCD) and the Low FODMAP diet.
A note from Cleveland Clinic
If you suffer from gastrointestinal symptoms — bloating and gas, cramping and indigestion — you've probably tried to self-diagnose and discovered how tricky that can be. So many symptoms and conditions overlap that even common causes, such as SIBO, can be hard to pin down. Medical testing can help sort out the causes of your distress. You can also learn a lot by adjusting your diet and observing how the changes affect your symptoms. For some people, a lifestyle change may be all it takes to manage symptoms of SIBO. If that isn't enough, you may need antibiotics — but you’ll have to be careful to rebuild a healthy gut in the weeks that follow to prevent SIBO from recurring.
Last reviewed by a Cleveland Clinic medical professional on 09/19/2021.
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