What is it?

It is normal for bacteria to live in your gastrointestinal (GI) tract. Actually, there are 10 times more bacterial cells in your body than your actual cells! There are about 500 different bacteria types that live in the GI tract. Typically, quite a few bacteria live in your colon, but not too many that live in your small intestine. The small intestine has less because of the constant motion pushing food along and from the acid that enters from the stomach. In this condition, there is an overgrowth of bacteria, both “good” and “bad”, in the small intestine leading to increased breakdown of food, inflammation, and trouble absorbing nutrients. This causes symptoms such as bloating, abdominal discomfort, diarrhea, and weight loss.

Who gets it?

The types of bacterial that live in your GI tract is impacted by the foods you eat, the region you live in, your stress, and the medications you use. Patients who have had bowel surgeries are also at increased risk. Several disorders are linked such as short bowel syndrome, motility disorders (these can be associated with diabetes, scleroderma, previous radiation, Crohn’s disease), chronic pancreatitis, connections between near and far parts of the intestines (fistulas), a weakened immune system, low levels of stomach acid, or liver disease such as cirrhosis. It is also more common in the elderly and people who are overweight.

Why does it happen?

There are normally a few different ways that your body prevents the extra growth of bacteria in the small intestine. This includes stomach acid, bile, digestive juices, a mucus layer that traps bacteria, muscle contractions of the small intestine moving things forward, the ileocecal valve (tissue that separates the large and small intestines and prevents backflow of material from the colon into the small intestine), and the immune system. The last part of the small intestine, the ileum, is the dividing point between the few bacteria in the upper GI tract and the many in the colon.

What are the symptoms?

Symptoms are variable and depend on the cause of the overgrowth and how significant it is. Symptoms may include:

  • Bloating
  • Increased gas
  • Nausea
  • Abdominal discomfort
  • Watery diarrhea
  • Lack of appetite
  • Weight loss

How is it diagnosed?

You may have a blood draw for laboratory tests. Imaging of your GI tract may be ordered. Examination of the tissue of the GI tract itself with an upper endoscopy or colonoscopy may be obtained. Some of the material from the jejunum, the middle part of the small intestine, may be obtained to analyze. The number of bacteria present in this sample can determine if there is overgrowth.

Breath tests work based on eating or drinking a substance; if bacteria are present in the small intestine, these substances will be broken down. The products of breakdown can be measured in your breath. Often these levels would rise once the substance reaches your colon, if there is also an earlier rise it is likely due to bacterial being present in the small intestine. There are several different possible tests, a labeled sugar ([14C]-d-xylose) or carbohydrate (usually lactulose or glucose). To make sure the test is not altered by your normal behaviors make sure to follow the directions provided. Often this means avoiding breads, pasta, or fiber for a period, no smoking for 2 hours prior to testing and you may get mouthwash just prior to the procedure. The test may not be accurate if you have lung disease.

Some providers will treat for this disorder if they think it is present as a way for testing for it. If symptoms resolve with treatment, great! This can be a tricky way of doing things though as treatment requires antibiotics. All antibiotics come with their own side effects, some of which might be similar to symptoms of bacterial overgrowth.

How is it treated?

The goal is not to rid the GI tract of all bacteria because some of these bacteria are important for the normal function of the gut, the immune system, and digestion. When symptoms are present, treatment, but not extermination, is necessary.

If surgery was the cause of the overgrowth, sometimes a repeat surgery is the only option; however, if other options are available and feasible, trials are appropriate.

First, any causes of slowing of GI movement should be removed such as narcotic pain medications and benzodiazepines. A prokinetic agent could be considered like metoclopramide or erythromycin.

Dietary changes can be made to consume nutrients that your body can readily absorb so there is less residual food left over for the bacterial. A high fat, low carbohydrate, low fiber diet is recommended. Fat is not significantly used by bacteria and also provides extra calories for you. Carbohydrates are avoided because they are the main source of nutrients for bacteria. Also, lactase levels are often reduced; this is the chemical the body uses to help break down lactose the sugar found in dairy products. Early in the course of treatment, avoid foods with lactose.

Most people will require treatment with antibiotics. The goal is to decrease the number of bacteria present in the small intestine. Typically, the antibiotics will be taken for 7-10 days. The improvement in symptoms can last for months, but some people need a longer course of antibiotics, up to two months, before feeling any better. Return of symptoms can also happen and retreatment with antibiotics is necessary. Some people need scheduled antibiotics such as the first 5-10 days every month or every other week. If this is the case, the antibiotic that is used will be rotated to prevent resistance.


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