Small Bowel Bacterial Overgrowth: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Small Bowel Bacterial Overgrowth?
A gastroenterologist usually treats small bowel bacterial overgrowth. This specialist can order breath tests, prescribe treatment, and check for other gut conditions. A primary care doctor often makes the first referral. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What it is
Small bowel bacterial overgrowth, often called SIBO, happens when too many bacteria grow in the small intestine. These bacteria are normal in the large intestine but cause trouble when they multiply in the small intestine, interfering with digestion and causing gas, bloating, and poor nutrient absorption.
Symptoms
The most common symptoms are belly pain, bloating, gas, and diarrhea. Some people feel full quickly or lose weight without trying because nutrients are poorly absorbed. Long-lasting problems can lower vitamin levels, especially vitamin B12.
Causes and who gets it
The small intestine normally has fewer bacteria than the large intestine. Gut movement, stomach acid, and intestinal valves keep numbers low; when these defenses weaken, bacteria build up. Risk is higher after abdominal surgery, with slowed gut movement such as diabetes, structural problems, or weakened immunity. Older adults are affected more often, and sometimes no cause is found.
How doctors diagnose it
Doctors start with a medical history and physical exam. A common test is a breath test: the patient drinks a sugary liquid and breathes into a container at set times so gases made by bacteria can be measured. Sometimes doctors take a fluid sample during an endoscopy.
Treatment
Treatment aims to lower the bacteria and fix the underlying cause when one is found. Doctors often prescribe antibiotics, and some people need more than one round because symptoms can return. Diet changes may help, such as smaller meals or fewer fermentable carbohydrates, and vitamin supplements may be needed.
When to see a doctor
Anyone with ongoing belly pain, bloating, diarrhea, or unplanned weight loss should see a doctor rather than guess. Seek care quickly for blood in the stool, severe pain, fever, or signs of dehydration such as dizziness and very dark urine.
How a direct primary care or concierge doctor fits in
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Either can be a good first stop, and longer appointments help when symptoms are vague. They can order lab work, suggest a breath test, prescribe antibiotics, and refer severe or persistent cases to a gastroenterologist.
Common questions
Is SIBO the same as irritable bowel syndrome?
No, they are different conditions, but the symptoms overlap a lot. Some people diagnosed with irritable bowel syndrome turn out to have bacterial overgrowth. Irritable bowel syndrome is a common condition causing belly pain and bowel changes. Doctors may test for it when IBS symptoms are severe or do not improve.
Does SIBO come back after treatment?
It can. Many people feel better after antibiotics. But symptoms return for some of them, especially if the underlying cause was not fixed. Doctors may repeat treatment or look for other problems.
Can diet alone cure it?
Diet changes can ease symptoms. But they usually do not remove the excess bacteria on their own. Most treatment plans combine diet with medicine. Always talk to a doctor before making big diet changes.
Is SIBO contagious?
No. It is an overgrowth of bacteria that are already in the body. It cannot spread from person to person.
Sources
- MedlinePlus - Small Intestine Diseases
- American College of Gastroenterology - Small Intestinal Bacterial Overgrowth (SIBO)
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
