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SIBO: Small Intestinal Bacterial Overgrowth Explained

Why too much bacteria in the small intestine causes bloating and gas, and how it is tested and treated

June 30, 2026 By Dr. Amber Khan, MD 7 min read

SIBO stands for small intestinal bacterial overgrowth. It happens when too many bacteria build up in the small intestine, where there should only be a small number. Those extra bacteria ferment food too early and produce gas, which leads to bloating, discomfort, and changes in bowel habits. SIBO often gets mistaken for other conditions, so it is worth understanding what it is and how it is treated.

What SIBO Is

Most of the bacteria in your gut belong in the colon. The small intestine, where food is digested and absorbed, normally has far fewer. When bacteria move up or overgrow in the small intestine, they feed on your food before your body can, and the gas they make causes the classic symptoms.

Symptoms

  • Bloating, often worse as the day goes on
  • Excess gas
  • Belly pain or cramping
  • Diarrhea, constipation, or both
  • Feeling full quickly
  • In longer-standing cases, weight loss or nutrient deficiencies

What Causes It

SIBO usually develops when something slows or changes the normal flow through the small intestine. Common reasons include slow gut motility, past abdominal surgery, and certain conditions such as diabetes or scleroderma. Low stomach acid and the frequent use of some medications can also play a part.

The Link to IBS

Many people with IBS, especially the type with bloating and diarrhea, turn out to have SIBO as part of the picture. This is one reason bloating that does not respond to the usual steps is worth a closer look.

How It Is Diagnosed

The most common test is a breath test. You drink a sugar solution and breathe into a device over a few hours, which measures the gases that bacteria produce. A rise in those gases points to overgrowth. Your history and symptoms guide whether the test makes sense for you.

Treatment

Treatment has a few parts that work together:

  • Antibiotics to reduce the overgrowth, often a type that stays mostly in the gut.
  • Treating the underlying cause, since fixing what allowed SIBO to develop is what keeps it from coming back.
  • Diet changes, such as a low-FODMAP approach for a period, which can ease symptoms while the gut settles.

Preventing It From Coming Back

SIBO can return, especially if the underlying cause is still there. Staying on top of gut motility, spacing meals to let the small intestine clear between them, and managing related conditions all help. If your bloating keeps returning, it is worth working with a gastroenterologist to find and treat the root cause rather than chasing symptoms.

Talk to a Gastroenterologist in Mountainside, NJ

If your symptoms keep coming back or you are not sure what is causing them, Dr. Amber Khan can help. We see patients from across Union County and New Jersey.