DR. THOMAS BACHARACH

Specialist in General Medicine

🕑 Reading time: 3–5 minutes

👆 Key points at a glance

• SIBO (Small Intestinal Bacterial Overgrowth) describes the excessive colonisation of bacteria in the normally sparsely populated small intestine. This leads to symptoms such as bloating, distended abdomen, diarrhea and constipation.
• The mislocated bacteria use specific substances from the diet and metabolise them. This can worsen the symptoms.
• For symptom control, a diet that temporarily avoids this specific form of carbohydrates is therefore useful. Which foods are included is discussed below.

Bacterial overgrowth (SIBO) caused by hydrogen-producing bacteria and what you can do about it

Contents
1. What is SIBO (Small Intestinal Bacterial Overgrowth)?
2. Which types of SIBO exist?
3. What is hydrogen SIBO?
4. Symptoms of hydrogen SIBO
5. Treatment of hydrogen SIBO
5.1 Antibiotics
5.2 Herbal therapies
5.3 Nutrition
6. Summary
7. FAQs

1. What is SIBO (Small Intestinal Bacterial Overgrowth)?

Under the diagnosis “SIBO (Small Intestinal Bacterial Overgrowth)” an excessive proliferation of intestinal bacteria in the small intestine is understood. This leads to irritable bowel–like symptoms. The mislocated bacteria ferment certain carbohydrates and fibres from food and form gases. The symptoms differ depending on the type of bacteria that have colonised the small intestine. Common symptoms include bloating, constipation, brain fog, diarrhea and abdominal pain. Diagnosis is made via a breath test with glucose or lactulose (increase of H₂ ≥20 ppm ≤90 min). In the case of methane producers, the more precise diagnosis is “IMO (Intestinal Methanogen Overgrowth)”. These can also colonise the large intestine.

Digestive chaos? SIBO is often the cause.

SIBO (Small Intestinal Bacterial Overgrowth) is often overlooked, even though millions suffer from bloating, pain, diarrhea or constipation.

Dr. Thomas Bacharach was affected himself. He shares his knowledge to show those affected what is really happening in the body.

Learn more

2. Which types of SIBO exist?

Depending on the type of intestinal bacteria that overgrow the gut, the diagnoses hydrogen SIBO (H2-SIBO), methane SIBO (IMO) and hydrogen sulfide SIBO (ISO) are distinguished. The differentiation can be made via the breath test. Depending on which gas increases in the breath test (methane or hydrogen), a different overgrowth is present. Hydrogen sulfide SIBO cannot yet be detected in Europe by measuring the increase in hydrogen sulfide in a breath test. Here it is only indirectly detectable by a so-called “flat-line test”. The flat-line test in hydrogen sulfide SIBO is an indirect diagnostic approach using the conventional lactulose breath test. After ingestion of a test solution, exhaled air is analysed for hydrogen and methane over about 180 minutes. If there is no typical increase in gases (“flat line”) during the entire course of the test, the symptoms and the absence of a gas rise suggest dominant production of hydrogen sulfide (H₂S) by specific bacteria – because H₂S is usually not detected by standard devices in Germany. The flat line therefore indicates that lactulose is metabolised so completely by H₂S-producing bacteria that hydrogen and methane are not detectable in the breath – an indirect sign of hydrogen sulfide SIBO.

3. What is hydrogen SIBO?

In hydrogen SIBO, intestinal bacteria that primarily produce hydrogen have colonised the small intestine. These include Escherichia coli (E. coli), which are often responsible for hydrogen production through fermentative metabolic processes in the small intestine. Klebsiella, which are known for hydrogen production and are frequently associated with symptoms such as diarrhea and bloating. Gram-positive aerobes such as Streptococcus, Bacteroides and Aeromonas also play a role. In addition, some Lactobacillus species can miscolonise the small intestine.

4. Symptoms of hydrogen SIBO

Typical symptoms of overgrowth with hydrogen-producing intestinal bacteria

• Bloating and a distended abdomen

• Diarrhea, often very watery

• Abdominal cramps and pain

• Unpleasant abdominal noises and a feeling of fullness

• Foul-smelling flatulence

• Fatigue, concentration problems (“brain fog”) and exhaustion

• Sometimes loss of appetite and unexplained weight changes

• Possible deficiency of specific vitamins and nutrients (especially vitamin B12 and fat-soluble vitamins (A, D, K, E))

The miscolonising bacteria in the small intestine ferment undigested carbohydrates and thereby produce increased amounts of hydrogen gas and short-chain fatty acids. These fatty acids draw water into the intestine osmotically, which leads to soft stools or diarrhea. Gas production causes bloating and abdominal cramps by stretching the intestinal wall. In addition, the bacteria can alter bile acids, which also affects digestion and stool consistency. The altered microbiota and inflammatory processes can trigger systemic symptoms such as fatigue and concentration problems. These symptoms differ from methane SIBO, which is more associated with constipation, whereas hydrogen SIBO more often tends to cause diarrhea.

5. Treatment of hydrogen SIBO

Various approaches are available for the treatment of SIBO:

5.2 Herbal therapies

Herbal antimicrobial substances such as oregano oil and pomegranate extract are frequently used specifically for hydrogen SIBO. They can be an alternative or supplement to antibiotics. The prebiotic PHGG (partially hydrolysed guar gum) is also often used in addition to antibiotic therapy.

5.3 Nutrition

A low FODMAP diet or a SIBO-specific diet reduces fermentable carbohydrates that serve as food for the bacteria. The goal is to reduce symptoms such as abdominal pain, bloating and diarrhea. In special, very severe cases, an elemental diet can be used to reduce bacterial colonisation.

5.4 Aftercare and lifestyle

After acute treatment, measures to maintain intestinal balance are important, such as the use of probiotics or prebiotics. Stress management and optimised gut motility should also be considered. Individual medical supervision is essential for optimal therapy selection and monitoring. Supplementation with specific vitamins and nutrients can also be useful in the course of treatment, as overgrowth may lead to deficiencies in certain vitamins and nutrients.

6. Summary

Hydrogen SIBO refers to the overgrowth of the small intestine with hydrogen-producing bacteria. Typical symptoms are mainly diarrhea, bloating, gas as well as brain fog and fatigue. Treatment is carried out with specific antibiotics (mainly rifaximin) or herbal agents such as oregano and pomegranate extract. To reduce symptoms, an adjustment of the diet (low FODMAP) is recommended. It is important to limit the duration of such a diet, otherwise the gut microbiome may be negatively affected.

7. FAQs

Sources

1. 1. Merck & Co., Inc. (2025). Small intestinal bacterial overgrowth (SIBO). In MSD Manuals Professional Edition. Retrieved from https://www.msdmanuals.com/de/profi/gastrointestinale-erkrankungen/malabsorptionssyndrome/dünndarm-bakterienüberwucherung-sibo
   2. Merck & Co., Inc. (2025). Small intestinal bacterial overgrowth – digestive disorders. MSD Manuals Consumer Edition. Retrieved from https://www.msdmanuals.com/de/heim/verdauungsstörungen/malabsorption/dünndarmfehlbesiedlung-ddfb ​
   3. Institut für Mikrobiologie und Diagnostik Berlin (IMD). (2019). Small intestinal bacterial overgrowth (SIBO): diagnostic information. Retrieved from https://www.imd-berlin.de/fachinformationen/diagnostikinformationen/300-399/372-duenndarmfehlbesiedlung-sibo