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Quick Facts

Bacterial Overgrowth Syndrome


The Manual's Editorial Staff

Last full review/revision Jul 2020| Content last modified Jul 2020
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Your gastrointestinal (GI) tract is the tube that goes from your mouth to your anus. The GI tract includes your esophagus (food pipe), stomach, and small and large intestines. Your intestines are where food is absorbed. Good bacteria live in your intestines. You need the right amount of these good bacteria.

What is bacterial overgrowth syndrome?

Bacterial overgrowth is when the good bacteria in the small intestines grow too much. The extra bacteria keep you from absorbing all the nutrients in your food. Not absorbing nutrients is called malabsorption.

  • The extra bacteria in your intestines keep you from digesting food properly

  • The bacteria also use up nutrients in your food that you need for your health

  • Some people have no symptoms, but others have diarrhea, lose weight, or feel gassy and bloated

  • Doctors may do a breath test, test samples of fluid from your small intestine, or do x-rays of your GI tract

  • Doctors treat bacterial overgrowth syndrome with antibiotics and may suggest changes in your diet

What causes bacterial overgrowth syndrome?

Bacterial overgrowth syndrome is mainly caused by:

  • Conditions that slow down your GI tract, which keeps your intestines from flushing out extra bacteria

The most common cause of a slow-down is:

Other diseases that can cause a slow-down include an underactive thyroid (hypothyroidism), systemic sclerosis, and amyloidosis.

Certain types of surgery on your intestines and complications of surgery also can cause bacterial overgrowth.

What are the symptoms of bacterial overgrowth syndrome?

Some people have few symptoms or only weight loss.

Common symptoms are:

  • Diarrhea that is greasy and smelly

  • Belly pain

  • Bloating

  • Passing more gas than usual

  • After months and years, vitamin and mineral deficiencies

Vitamin and mineral deficiencies can cause:

  • Low blood count (anemia)

  • Easy bruising

  • Tingling of hands and feet

How can doctors tell if I have bacterial overgrowth syndrome?

Doctors diagnose bacterial overgrowth syndrome based on your symptoms and if you have conditions that favor overgrowth of bacteria in your colon. They may also:

  • Look down your stomach and intestines with a flexible viewing scope (endoscopy)

  • Measure certain chemicals in your breath

  • Take x-rays of your stomach after you swallow a liquid contrast agent

How do doctors treat bacterial overgrowth syndrome?

Treatments can include:

  • Antibiotics

  • Eating less carbohydrates and fiber

  • Vitamins or minerals to correct specific deficiencies

Most people get better after taking antibiotics for 10 to 14 days.

Doctors may suggest you eat a diet that's higher in fat and lower in carbohydrates and fiber to slow down the bacteria's regrowth.

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Loss of Smell
Anosmia is the total loss of smell. Most people with anosmia can taste sweet, sour, salty, and bitter substances but cannot distinguish among specific flavors. This is because the sense of smell makes it possible to distinguish among flavors, not taste receptors as many people erroneously believe. Which of the following is NOT a common cause of anosmia?
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