SIBO stands for ‘small intestinal bacterial overgrowth.’ It means that there are too many bacteria in the small intestine.
Your gut contains trillions of bacteria that support your health. But these aren’t evenly spread out – the vast majority live in your large intestine, towards the end of your gut.
Your small intestine is connected to your stomach. In people with SIBO, this section has a larger population of bacteria than is typical.
Often, SIBO is caused by food moving more slowly than usual through your intestines.
SIBO can have a range of effects, including gut symptoms such as bloating, excess wind, diarrhoea, pain and feelings of fullness.
More severe cases of SIBO can cause difficulties digesting or absorbing nutrients. The result may be deficiencies and steatorrhoea (fatty poop), which can lead to weight loss and undernutrition.
Below, we’ll outline more of SIBO’s symptoms, including changes in your stool. We’ll explain when to seek help and describe the diagnostic process, as well as SIBO’s causes and treatments.
Symptoms of SIBO
If you have SIBO, the excess bacteria in your small intestine digest carbohydrates that you eat. This produces gas, which can cause some of SIBO’s symptoms, like belching and bloating.
As we’ve mentioned, SIBO can lead to nutrient deficiencies if it's left untreated in the long term. This is because the bacteria in your small intestine can consume nutrients, like vitamin B12, before your body has time to absorb them.
The bacteria can also consume bile salts, which you produce to break down fats. As a result, your body may absorb less fat, which can lead to fatty poop. You may also be less able to absorb fat-soluble vitamins, like vitamin D.
Common symptoms of SIBO include:
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excess flatulence and belching
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uncomfortable fullness after a meal
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a lack of appetite
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abdominal pain or distension (stretching)
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unexplained weight loss
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fatigue and weakness
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nausea
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diarrhoea or constipation
Changes to your stool
You may notice changes to your poo because SIBO can interfere with how your body handles fats.
When more fats come out in your poo, it may be:
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light in colour
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greasy
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particularly bad-smelling
When to visit your doctor
It’s normal to experience gut symptoms from time to time. But if they’re persistent and don't resolve within a few weeks, you should speak with your doctor.
It’s important to recognise what’s normal for you. If you notice gut symptoms or changes in your poo habits that you can't explain, it’s best to seek help.
What causes SIBO?
SIBO can develop for a range of reasons, including:
1. Abdominal surgery
Surgery can lead to ‘adhesions’, bands of scar tissue that can make internal surfaces stick together.
Adhesions can slow the passage of food through your gut, increasing the likelihood that bacteria will find a home in your small intestine.
2. Structural problems
Changes to the structure of your intestines alter its function. This can disrupt the balance of bacteria by creating new nooks and crannies for gut bacteria to inhabit.
Some structural changes include:
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Small bowel obstructions: These blockages in your small intestine may be strictures or tumours.
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Small bowel diverticulosis: Small pouches develop in your small intestine’s lining.
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Gastrointestinal fistula: This is an abnormal tunnel or opening.
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Blind loop syndrome: Food can’t pass through your intestines in the usual way, so it bypasses a section of the intestines.
3. Other medical conditions
Some health issues can affect how quickly food moves through your gut.
These changes in speed (motility) can increase the risk of developing SIBO. When food moves more slowly, bacteria are more likely to set up shop.
Medical conditions that can affect motility include:
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diabetes
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pancreatitis (inflammation of the pancreas)
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inflammatory bowel disease (IBD)
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kidney failure
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liver damage
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hypothyroidism (the thyroid not producing enough hormones)
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gastroparesis (food passing too slowly from the stomach into the intestines)
Also, problems with the immune system, like lupus or scleroderma, can increase the risk of SIBO when the immune system finds it difficult to manage bacterial populations.
4. Low stomach acid
Stomach acid plays many roles, one of which is helping to prevent bacteria from travelling from your stomach into your small intestine.
So, if you don’t produce enough stomach acid, more bacteria can make it through, increasing the risk of SIBO.
Factors that can reduce stomach acid production include:
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Ageing: Acid production generally slows down.
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Stress: Long-term, continuous stress has this effect.
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Medications: This is especially true for heartburn or acid reflux treatments.
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Helicobacter pylori infection: This common bacterial infection can cause stomach ulcers.
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Zinc deficiency: Zinc is necessary for producing stomach acid.
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Gastric bypass surgery: A smaller stomach naturally produces less acid.
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Autoimmune gastritis: This inflammatory condition causes the body to attack the stomach’s lining.
5. Some medications
As we note above, acid reflux and heartburn medications can reduce stomach acid. In fact, the use of drugs called proton pump inhibitors (PPIs) is among the most common causes of low stomach acid.
PPIs are a common treatment for gastroesophageal reflux disease, known as GERD or GORD. Because these drugs suppress stomach acid, they can increase the risk of SIBO.
Other medications can increase SIBO risk in different ways. For example, the repeated use of antibiotics can alter the balance of your gut bacteria populations. However, antibiotics are also a treatment for SIBO.
Meanwhile, taking opioids for pain relief can interfere with your gut motility.
Do any foods make SIBO worse?
Foods themselves don’t cause SIBO, but some might make the symptoms worse. Among these culprits are foods that contain fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs).
FODMAPs are compounds that bacteria in the small intestine can ferment. As bacteria break them down, they produce gases, which can cause symptoms like bloating and excess wind.
High-FODMAP foods include:
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grains, such as wheat, barley and rye
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many fruits, including cherries, apples, apricots and grapes
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many vegetables, such as cauliflower, mushrooms, onion, garlic and beetroot
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legumes and pulses
Your doctor may suggest a low-FODMAP diet if you have SIBO. While this may relieve symptoms, it won’t treat the underlying cause.
It’s important to have medical supervision on a low-FODMAP diet. A qualified professional, like a dietitian, can help make sure you're still getting enough nutrients.
How do doctors diagnose SIBO?
Diagnosing SIBO can be challenging. The symptoms overlap with those of other gut conditions, and other health issues often occur at the same time.
The most common approach is a breath test. As gut bacteria break down food, this produces gases like hydrogen and methane. Because someone with SIBO has more bacteria in their small intestine, closer to their mouth, a breath test can detect the excess gases.
Your doctor may also order a blood test to check for nutrient deficiencies and a stool test to detect undigested fats. In addition, they may run imaging tests to look for structural problems.
Treatments for SIBO
The most common treatment for SIBO is a course of antibiotics to eradicate the bacteria that aren’t supposed to be there.
For some people, a single course resolves the issue, while others may need long-term treatment.
Doctors may also prescribe vitamin and mineral supplements to address any nutrient deficiencies. And they may design a short-term diet or provide long-term nutrition advice.
Importantly, doctors also try to identify and address the underlying cause of SIBO, which will help determine the best treatment.
While some people respond to treatment within a few weeks, it may take months. And in some cases, SIBO returns after the treatment has finished.
Summary
SIBO means that there’s an overgrowth of bacteria in your small intestine. It can cause a range of symptoms, including excess wind, bloating, nausea, fatigue and changes to your poo.
A number of factors increase the risk of developing SIBO, including medical conditions, medications and abdominal surgery.
Doctors generally diagnose SIBO with a breath test, but they may need blood, stool or imaging tests.
Most often, the treatment involves taking antibiotics. While one course of antibiotics may work for some, others may need longer-term treatment.
To learn more about other gut health topics, visit Symprove’s Gut Hub.
Sources
Autoimmune gastritis. Nature Reviews Disease Primers. (2020). Link.
Blind loop syndrome. StatPearls. (2022). Link.
Diet and intestinal bacterial overgrowth: Is there evidence? World Journal of Clinical Cases. (2022). Link.
Meta-analysis: Proton pump inhibitors moderately increase the risk of small intestinal bacterial overgrowth. Journal of Gastroenterology. (2018). Link.
Postoperative ileus. StatPearls. (2023). Link.
Show me what you have inside — the complex interplay between SIBO and multiple medical conditions — a systematic review. Nutrients. (2023). Link.
Small bowel diverticulosis and malrotation: A new spin on SIBO. The American Journal of Gastroenterology. (2022). Link.
Small intestinal bacterial overgrowth. Gastroenterology and Hepatology. (2007). Link.
Small intestinal bacterial overgrowth: Clinical features and therapeutic management. Clinical and Translational Gastroenterology. (2019). Link.
Small intestinal bacterial overgrowth in patients with lower gastrointestinal symptoms and a history of previous abdominal surgery. JAMA Surgery. (2011). Link.
Small intestinal bacterial overgrowth (SIBO). (2024). Link.
Small intestinal bacterial overgrowth syndrome. World Journal of Gastroenterology. (2010). Link.
Symptomatic response to antibiotics in patients with small intestinal bacterial overgrowth: A systematic review and meta-analysis. Journal of Neurogastroenterology and Motility. (2024). Link.
The impact of alcohol consumption and cholecystectomy on small intestinal bacterial overgrowth. Digestive Diseases and Sciences. (2013). Link.
