Small Intestinal Bacterial Overgrowth (SIBO)

What is SIBO?

Small intestinal bacterial overgrowth (SIBO) happens when bacteria that are usually found in the digestive system grow and multiply in the small intestine. These bacteria can cause digestive symptoms from the breaking down (fermentation) of digestive food and can make it hard for you to digest food properly and to absorb nutrients. 

Your small intestine has a normal population of bacteria but SIBO can happen when your digestive system works slowly, so food stays in it for longer and bacteria has a chance to over grow. 

These bacteria convert the carbohydrates you eat into gas, use up protein and some vitamins your body needs, and consume the bile salts that help your digestion.

Symptoms of SIBO

With small intestinal bacterial overgrowth, also called blind loop syndrome, you may notice SIBO symptoms like:

• Loss of appetite
• Bloating
• Nausea
• Diarrhea
• Gas or bloating, especially after a meal
• Feeling uncomfortably full after a meal
• Belly (abdominal) pain or cramping
• Constipation
• Smelly, oily or floating stools
• Malnutrition/malabsorption
• Fatigue or weakness
• Unintentional weight loss

You should schedule an appointment with a health care provider if symptoms like bloating, diarrhea, abdominal pain or fatigue last for more than a few days. If you have unexplained weight loss, severe abdominal pain or signs of malnutrition such as brittle nails, thinning hair or anemia, talk to a provider right away.

Untreated, SIBO can cause nutritional deficiencies and complications such as:

• Vitamin deficiency, especially vitamins A, B12, D, E and K.
• Osteoporosis (weak, brittle bones)
• Kidney stones
• Leaky gut, where toxins and bacteria can enter the bloodstream from the digestive system
• Dehydration
• Excess bleeding
• Liver disease

SIBO causes and risk factors

Your risk of SIBO is higher as you get older, because you’re more likely to have medical conditions or need to take medications that slow your digestion. You may be more likely to develop small intestinal bacterial overgrowth if you have:

• Structural issues like pouches in the intestine (small bowel diverticula) or narrowing (strictures) that can cause bacteria to build up.
• An abnormal connection (fistula) between different parts of your digestive system.
• Previous gastrointestinal surgeries that disrupt movement through your small intestine causing blockages, or radiation therapy or injury to the small intestine, which can cause scar tissue.
• Conditions such as Crohn’s disease, irritable bowel syndrome (IBS), gastroparesis, diabetes, celiac disease, lupus, pancreatitis, AIDS, kidney failure, liver disease, low levels of thyroid hormones, Parkinson’s disease or scleroderma.
• Low stomach acid from using proton pump inhibitors (PPIs) for a long time, H. pylori infection or gastric bypass surgery.
• Slow movement of food through the digestive system due to medication such as narcotics.

Diagnosing SIBO

Your provider will talk to you about your medical history and perform a physical exam. They may recommend these tests for SIBO diagnosis:

• Hydrogen/methane breath test: For this test, also called the lactulose breath test, you drink a special sugar solution. Then, every 15 minutes for two hours, you breathe into a device that measures gas levels. High levels of hydrogen or methane indicate bacterial overgrowth.
• Blood tests: These tests may show vitamin deficiencies.
• Stool sample: A stool test may show if you’re not digesting fat properly.
• Imaging tests: X-rays, CT scans or MRIs may show structural problems in the small intestine.
• Endoscopy and biopsies: In certain instances, your provider may examine your small intestine with a thin, flexible tube that goes down your throat and through your digestive tract to your small intestine. With this procedure, they can take samples of tissue and fluid to test them for bacteria in a lab.  Currently, this procedure is mostly used by certain institutions for research purposes only.

Conditions commonly mistaken for SIBO

These conditions have symptoms that may overlap with small intestinal bacterial overgrowth:

• Irritable bowel syndrome: IBS and SIBO may both cause bloating, diarrhea and abdominal pain. Up to one-third of people diagnosed with IBS may actually have SIBO.
• Lactose Intolerance: Difficulty digesting lactose, the sugar found in milk, can cause bloating, gas and diarrhea, But with SIBO, eating other foods may also cause symptoms.
• Celiac disease: Both SIBO and celiac disease can cause nutrient deficiencies and digestive discomfort. You may need testing for both conditions if symptoms overlap.
• Crohn’s disease: Crohn’s and SIBO both cause diarrhea and abdominal pain, but inflammation of the digestive tract causes Crohn’s while bacterial overgrowth causes SIBO.
• Gastroparesis or chronic constipation: With these conditions, your digestive system works slowly, which can cause bloating and discomfort like SIBO does.

If you’ve been diagnosed with any of these digestive conditions, you may want to talk to your provider about testing for SIBO. It’s important to have an accurate diagnosis. Without the right diagnosis, you could have treatments that don't address what’s causing your symptoms.

Treatment options for SIBO

Medication, changes in your diet and treating other conditions can help in SIBO treatment.

Medication

Antibiotics can reduce the overgrowth of bacteria. Sometimes, your provider might recommend a one- to two-week course of antibiotics even without testing, if your symptoms make SIBO likely.

Your provider may recommend rifaximin (Xifaxan), since it mainly targets gut bacteria without much effect on the rest of the body. Metronidazole (Flagyl) and other antibiotics are also often prescribed. If you have the type of SIBO that produces methane instead of hydrogen, you may need a combination of the antibiotics rifaximin and neomycin.

Your provider may recommend medication that speeds up your digestive system. If you have severe weight loss from SIBO, you may need vitamin B12 injections and vitamin, calcium and iron supplements.

Diet changes

After antibiotics reduce the overgrowth of bacteria, changes in your diet can help keep it from coming back. Smaller, more frequent meals can keep you from having too much food in your stomach.

You may want to try a lactose-free diet or the low-FODMAP diet, which limits certain fruits, vegetables and grains that ferment in the gut and feed bacteria.

Another option, the specific carbohydrate diet (SCD), eliminates certain sugars and starches. The SCD diet may be easier to follow in the long term. A dietitian can help you come up with an eating plan that works for your lifestyle while keeping SIBO from returning.

Talk to your provider if you’re considering trying probiotics or prebiotics. They may help balance your gut microbiome, but some probiotics may worsen symptoms, depending on the type of bacteria in your gut. Using them after antibiotic treatment is finished could help promote a healthy balance of gut bacteria.

Treating other conditions

You’ll also want to make sure you treat any conditions that might lead to bacterial overgrowth. For example, if you have IBS, treatments like prokinetics may speed up your digestive system and reduce the risk of SIBO. For structural issues, you may need surgery.

Getting care

If you have digestive discomfort or unexplained symptoms, Banner Health can help. Our experienced gastroenterologists, dietitians and specialists work together to create a personalized care plan that meets your needs.

Because accurate diagnosis is so important, we use state-of-the-art diagnostic tests, including hydrogen/methane breath test services to diagnose SIBO and endoscopy and lab services to rule out other conditions with similar symptoms. Our targeted treatments help keep SIBO from coming back and help your digestive system stay healthy.