Understanding breath test SIBO results

Overview

The breath test for SIBO (Small Intestinal Bacterial Overgrowth) is a simple, non‑invasive test that measures the amount of hydrogen and methane gas in your breath after you drink a sugar solution. High levels of these gases can suggest that there are too many bacteria living in your small intestine, which can cause digestive symptoms.

SIBO is a recognised condition, but it is not extremely common. It may affect up to 10–20% of people with certain digestive disorders, such as irritable bowel syndrome (IBS).

SIBO can affect people of any age, but it is more common in people with slowed gut movement, acid‑reducing medications, previous abdominal surgery, or conditions like diabetes, Crohn’s disease, or coeliac disease.

Symptoms

Causes

Main causes

• Motility problems – the small intestine does not move food and bacteria along properly.
• Low stomach acid – from medications or ageing, allowing bacteria to grow higher up.
• Structural issues – such as diverticula or surgical loops where bacteria can collect.
• Immune system problems – conditions like common variable immunodeficiency (CVID) can lead to SIBO.

Risk factors

• Long‑term use of acid‑reducing medications (e.g. proton pump inhibitors).

When to see a doctor

See a doctor urgently if:

• If you have sudden, severe belly pain.
• If you see blood in your stool or vomit.
• If you have a high fever and abdominal pain.

Book a routine appointment if:

• If you have ongoing bloating, gas, or changes in bowel habits for more than a few weeks.
• If you have unintentional weight loss or fatigue.

Diagnosis

A breath test for SIBO is usually arranged by a gastroenterologist or your GP. You will be asked to follow a special diet for 24 hours before the test, then breathe into bags every 20–30 minutes for 2–3 hours after drinking a sugar solution (lactulose or glucose). The breath samples are analysed for hydrogen and methane gas levels.

Tests that may be done

• Lactulose breath test (most common)
• Glucose breath test (alternative, may be used for certain cases)
• Sometimes additional tests like a stool test or blood work are done to rule out other causes.

What to expect at your appointment

The test is done in the clinic or occasionally at home. You will need to fast overnight. On the day, you blow into a bag to get a baseline reading, then drink the sugar solution. You blow into bags at set times. The whole process takes about 3 hours. There is no pain. You may feel a little bloated during the test, but this is normal. Your doctor will discuss the results with you.

Treatment

Treatment for SIBO focuses on reducing the overgrowth of bacteria, fixing the underlying cause if possible, and addressing any nutritional deficiencies. Your doctor will create a plan tailored to you.

Self-care at home

• Eat smaller, more frequent meals to reduce the burden on your gut.
• Avoid foods that ferment easily – such as beans, onions, garlic, wheat, and high‑fructose fruits – during the active phase (a low‑FODMAP diet may be recommended).
• Drink plenty of water between meals, not with meals.
• Chew food thoroughly and eat slowly.

Medical treatments

Doctors usually prescribe a course of antibiotics that act mainly in the gut to reduce bacterial numbers. These are not the same as antibiotics for other infections. The choice and length of treatment depend on which gas type was high in your test. Prokinetic medications (which help the gut move) may also be given to prevent the problem from coming back. Always follow your doctor’s advice – never take leftover antibiotics.

Living with this condition

Many people with SIBO find that symptoms improve with treatment, but the condition can come back. Learning which foods trigger your symptoms and sticking to a gut‑friendly diet can help you feel in control.

Lifestyle tips

• Keep a food and symptom diary to spot patterns.
• Manage stress with gentle exercise, mindfulness, or talking therapies – stress can worsen gut symptoms.
• Stay active – even a 20‑minute walk after meals can help move gas along.
• Get enough sleep – poor sleep affects gut motility.

Diet and exercise

A low‑FODMAP diet, followed for a short time with the help of a dietitian, can reduce bloating and discomfort. After treatment, you can slowly reintroduce foods. Gentle exercise like walking, yoga, or swimming can aid digestion without putting pressure on the belly.

Prevention

Since SIBO is often linked to an underlying condition, it cannot always be prevented. But you can lower your risk by keeping your gut moving well – eat fibre‑rich foods if you tolerate them, stay hydrated, and treat acid reflux without overusing acid‑suppressing medications. If you have diabetes, good blood sugar control may help.

Screening programmes

There is no routine screening for SIBO in the general population. Testing is done only if you have symptoms that suggest the condition.

Complications

If left untreated

• Malnutrition – your body may not absorb enough vitamins and minerals (especially vitamin B12, iron, and fat‑soluble vitamins).
• Unexplained weight loss.
• Osteoporosis (weak bones) due to poor calcium and vitamin D absorption.
• Worsening of underlying gut conditions, such as IBS or Crohn’s disease.

Long-term outlook

With the right treatment, most people’s symptoms improve significantly. The outlook is good – many people can return to a normal diet and live symptom‑free. However, SIBO can recur, so you may need to repeat treatment and stay mindful of your gut health. Your doctor will help you plan for long‑term management.

Find support

International organisations

• Guts UK
• World Gastroenterology Organisation

Local organisations

• NHS (UK) · United Kingdom
• Australian Gut Foundation · Australia

Helplines