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Bacterial Overgrowth Syndrome

Medically reviewed by Last updated on Aug 31, 2022.

What is bacterial overgrowth syndrome (BOS)?

BOS is a condition that causes too many bacteria to grow in your small intestine. You may have too many of one kind of bacteria, or several kinds of bacteria. Bacteria normally live inside your small intestine in a healthy balance. The bacteria are important for your health. Bacteria protect you against organisms that could make you sick. They also regulate your immune system, digestion, and electrolyte balance. Vitamin K, folate, and other nutrients are produced by bacteria. BOS can develop because you do not have enough stomach acid to destroy bacteria. Conditions that slow the movement of contents through your intestines can also lead to BOS. The slow movement allows the bacteria to sit in one place and continue to grow.

Digestive Tract

What causes BOS or increases my risk?

  • Diverticulosis, a bowel blockage, or a fistula (abnormal opening in your stomach or intestines)
  • A condition that affects how the intestines contract, such as diabetic neuropathy
  • Surgery on your digestive system
  • Certain medicines, such as opioids or medicines that control stomach acid
  • A medical condition such as liver disease, pancreatitis, or kidney disease
  • Older age or obesity

What are the signs and symptoms of BOS?

  • Diarrhea, abdominal pain, or nausea
  • Bloating, gas
  • Problems absorbing nutrients, or low vitamin or mineral levels, such as iron
  • Weight loss
  • Anemia (low red blood cell count)

How is BOS diagnosed?

Tell your healthcare provider about your symptoms and when they started. Tell him or her about all your current medicines. Also tell your provider about any surgery you had in your digestive system. You may also need any of the following:

  • A breath test may be used to check for signs of too many bacteria, such as hydrogen and methane gas. These are given off as bacteria break down carbs. Your body will get rid of them through your breath.
  • A fluid culture is used to take a sample of your small bowel fluid. The fluid is removed and tested to find the kind and number of bacteria it contains.
  • X-ray pictures may be used to check for certain problems in your intestines that can lead to bacterial overgrowth. Contrast liquid may be used to help problems show up better in the pictures. Tell the healthcare provider if you have ever had an allergic reaction to contrast liquid.

How is BOS treated?

  • Antibiotics are used to help your body get rid of extra bacteria. You may need more than one kind of antibiotic. Your healthcare provider may also change the kind of antibiotic to find one that works best for you.
  • Medicines may be used to help waste move through your intestines or empty your stomach more quickly.
  • Nutrition changes may be used to stop bacterial overgrowth, or to manage your symptoms. Bacteria eat sugar, so your healthcare provider may recommend a low-carb or lactose-free diet. Lactose is milk sugar, found in dairy products and certain other foods. Your provider or a dietitian can help you create meal plans with the right calories and nutrition. Your provider may also recommend vitamin or mineral supplements if your levels are low.
  • Treatment for the cause of your BOS may be needed. You may need to have surgery to fix a problem in your intestines. You may need medicines to treat conditions such as diabetic gastroparesis. Your healthcare provider may stop or change a medicine you currently take if it is causing BOS.

What can I do to manage or prevent BOS?

  • Drink more liquids to prevent dehydration. Dehydration can develop if you have diarrhea several times each day. Drink liquids as directed. You may also drink an oral rehydration solution (ORS). An ORS has the right amounts of water, salts, and sugar needed to replace body fluids. Ask your healthcare provider where to buy ORS and how much to drink.
  • Talk to your healthcare provider about diarrhea medicine. Your provider will tell you if it is safe to take medicine to control diarrhea. This depends on what is causing your BOS. You may need prescription medicine, or you may be able to take over-the-counter medicine. Follow directions so you do not make abdominal pain worse or develop constipation.
  • Ask about probiotics. Probiotics are also called good bacteria. They can help protect you from harmful bacteria. Ask your healthcare provider if probiotics are right for you. You may be able to eat yogurt or other foods high in probiotics. Your provider may instead recommend a pill or liquid form.
  • Limit alcohol. Alcohol can lead to BOS. Alcohol can also make abdominal pain worse. A drink of alcohol is 12 ounces of beer, 5 ounces of wine, or 1½ ounces of liquor.

When should I call my doctor?

  • You have irregular or fast breathing or a fast or pounding heartbeat.
  • You have a headache, dizziness, or confusion.
  • You are urinating less than usual or not at all.
  • You have a fever.
  • Your signs and symptoms do not go away, or they come back, even after treatment.
  • You suddenly lose weight without trying.
  • You are more tired than usual or weak.
  • You have questions or concerns about your condition or care.

Care Agreement

You have the right to help plan your care. Learn about your health condition and how it may be treated. Discuss treatment options with your healthcare providers to decide what care you want to receive. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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Further information

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