It’s not always nice to talk about digestion, but it’s important. And when things aren’t going smoothly, your gut feeling may get your attention.
Your digestive tract is home to trillions of bacteria, or living microorganisms. Together they form the so-called intestinal microbiome. This bacterial ecosystem is located primarily in your large intestine (also called your large intestine), but a small portion is found in your stomach and small intestine.
The word “bacteria” can raise some warning signs, but not all of them are harmful. However, too many bacteria – and the wrong kind – can cause some problems, such as small intestinal bacterial overgrowth (SIBO). This occurs when there are excessive bacteria in the small intestine.
Although it sounds simple, SIBO is far from it. SIBO can be difficult to diagnose and get to the cause of, and it’s not clear how many people it affects.
Here’s what’s currently known about SIBO so you can better understand it for yourself.
What is SIBO?
SIBO occurs when too many bacteria – particularly colonic bacteria from the large intestine – enter the small intestine.
Some bacteria in the small intestine is normal, but SIBO is a buildup of bacteria in the intestines, Dr. Ayanna Lewis, board-certified gastroenterologist and member of HealthyWomen’s Women’s Health Advisory Council. It is not only due to the excessive amount of bacteria, but also the presence of bacteria that are not normally found there. There are four different types of SIBO, including hydrogen dominant SIBO, intestinal methanogen overgrowth, mixed (also methane-hydrogen dominant), and hydrogen sulfide SIBO. The classification of the different types is based on which type of gas is caused by the overgrowth of bacteria in your intestines.
SIBO symptoms
SIBO affects the digestive tract, so many of the most common symptoms show up in the gut or in major changes to your toilet habits.
Common symptoms of SIBO include:
- Bloating or flatulence
- stomach pain
- Diarrhea
- discomfort
- gas
- Indigestion
- nausea
- Feeling of fullness
- Unintentional weight loss
“I felt like I had a brick in my stomach,” said Jill Joseph, a woman in her 50s who was diagnosed with SIBO after experiencing severe symptoms. “My symptoms included extreme bloating, almost daily diarrhea, and belching during and after meals.”
SIBO can get in the way of healthy digestion, which your body needs to use the nutrients from your food. As a result, you could experience malnutrition or nutrient deficiencies, especially vitamin B12 deficiency.
SIBO can also cause steatorrhea, or fatty stools. Too much fat in your stool can sometimes be a sign that you have this condition.
Risk factors for SIBO
Some are more likely to develop SIBO than others, including those with existing gastrointestinal problems. For example, patients with inflammatory bowel disease (IBD) are almost six times more likely to develop intestinal methanogen overgrowth (SIBO) than those without.
Researchers have also identified some additional risk factors, including diseases associated with SIBO:
SIBO is more common in women and those assigned female at birth (AFAB), and the incidence increases with age.
What causes SIBO?
“There’s usually a reason someone has developed this excess of bacteria in their gut,” Lewis said. “Often it’s due to a structural or motor problem.”
For example, SIBO is a possible complication of abdominal surgery. “It can be very common with cesarean sections (C-sections) or gallbladder surgeries,” Lewis said. Abdominal surgery can cause structural changes that can affect digestion and allow bacterial overgrowth in the small intestine.
As for motility, slowing or stopping digestion is thought to play a role in SIBO. For this reason, it is sometimes associated with blind loop syndrome – when food bypasses part of the intestines during digestion, sometimes as a complication of abdominal surgery. This also explains why SIBO can occur in people with constipation – slower digestion creates more opportunities for bacteria to linger and grow in the small intestine.
Taking combined oral birth control pills also increases the risk of developing SIBO, which may partially explain why the condition is more common in women and people with atrial fibrillation.
How to test for SIBO
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To determine SIBO as the cause of your symptoms, you typically start with a conversation with a healthcare provider (HCP). “SIBO can be diagnosed clinically based on symptoms,” Lewis said.
Tests are also available, including a breath test. Hydrogen and methane breath markers are the most commonly used test for SIBO. It’s non-invasive and involves drinking a sugar solution and measuring your breath for hydrogen and methane gases. This is how Joseph’s SIBO was diagnosed, even though she had to proactively ask her HCP for a test.
Other tests for SIBO may include:
- A small intestinal aspirate and fluid culture – an endoscope is inserted through the mouth into the small intestine to collect a sample of fluid for laboratory analysis.
- Blood test to check for any nutrient deficiencies.
- Stool fat test – a stool sample is tested for fat malabsorption.
- Imaging tests such as x-rays, computed tomography (CT), or magnetic resonance imaging (MRI) to identify structural abnormalities.
Although various tests are available, there is no gold standard for diagnosing SIBO.
As if diagnosing SIBO wasn’t difficult enough, the symptoms are fairly general and often overlap with other conditions. For example, SIBO symptoms can be the same as IBS symptoms. This can sometimes make it difficult to make an accurate diagnosis.
SIBO treatment
SIBO is usually treated with oral antibiotics. Your doctor may prescribe antibiotics for 10-14 days to reduce bacteria in the small intestine. In some cases, you may need to take several rounds of antibiotics to treat recurring symptoms, as SIBO is known to recur – something Joseph worries about.
A change in diet may also be necessary. Bacteria often feed on carbohydrates, so a diet high in fat and low in carbohydrates and fiber can be beneficial.
In Joseph’s case, her primary care doctor prescribed antibiotics and recommended a low-FODMAP diet. “This is to help prevent the bacteria from growing again,” Joseph said, adding that she started feeling better almost immediately after changing her diet.
What to do if you think you have SIBO?
Anytime you notice unusual changes in your toilet habits or experience symptoms that just won’t go away, it’s a good idea to let your doctor know what’s going on.
“These symptoms should always prompt you to see a gastroenterologist and undergo further testing,” Lewis said. “The purpose is to make sure there are no other underlying problems, such as an intestinal obstruction, that should not be ignored.”
Joseph’s personal journey took many twists and turns before she found a diagnosis, further illustrating how SIBO can be overlooked or misunderstood. Her most important advice to anyone suffering from SIBO symptoms: “Be your own advocate.”
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