Bacterial Overgrowth: SIBO, IMO and Excess Hydrogen Sulfide

In the complex world of gut health, small intestinal bacterial overgrowth (SIBO), intestinal methanogen overgrowth (IMO), and excess hydrogen sulfide stand out for their significant impact on digestive and systemic health. This article examines these conditions and provides information on diagnosis, dietary adjustments, supplements, and lifestyle changes necessary for treatment and recovery.

small intestinal bacterial overgrowth SIBO


SIBO, or small intestinal bacterial overgrowth, is when there are too many bacteria in the small intestine, which causes bothersome and often painful gastrointestinal symptoms. The small intestine usually has fewer bacteria than the colon. When there are too many bacteria in the small intestine, it disrupts the normal balance in the gut microbiome, which causes the symptoms of SIBO.

SIBO Symptoms

Patients with SIBO often experience the following symptoms one or more times a week for at least four weeks:

  • Bloating
  • Distension
  • Abdominal pain
  • Gas 
  • Flatulence
  • Diarrhea
  • Constipation

These symptoms can look like other illnesses. The most common symptom reported by patients with SIBO is bloating, often after eating.

What Causes SIBO

SIBO can be a tricky result of a number of different medications and conditions. Patients with irritable bowel syndrome (IBS) and suspected motility disorders are at a higher risk of developing SIBO. Many people don’t know that up to 80% of IBS patients could also have SIBO.

Other patients at risk may have experienced:

  • Structural damage, injury, or defects in the small intestine
  • Diabetes
  • Radiation therapy
  • Diverticulosis
  • Intestinal lymphoma
  • Crohn’s disease 
  • Scleroderma
  • Gastric surgery (obesity or ulcers)
  • Fistula 

Some surgeries can cause SIBO because food and waste can linger in the intestines due to impaired motility from the surgery. This means that there is now more food and waste for the bacteria in the gut to feed on, which causes them to colonize and multiply, resulting in bacterial overgrowth.

Which Gas Indicates SIBO

Some bacteria in the small bowel can produce too much hydrogen (H2). If you have too much hydrogen in your breath, it could mean you have SIBO.


Intestinal methanogenic overgrowth, or IMO, is when there’s an overgrowth of methane-producing archaea in the small and large intestines. This condition was previously called “methane SIBO,” but that term isn’t quite accurate. Methanogens aren’t bacteria (the “B” in SIBO), they’re archaea, which are a group of single-celled organisms lacking a defined nucleus. It’s also possible for these methanogens to overgrow in the colon, not just the small intestine (the “SI” in SIBO).

IMO Symptoms

Patients with IMO experience symptoms similar to SIBO, including abdominal pain, bloating, gas, distension, flatulence, and especially constipation. The level of methane measured by a breath test correlates with the severity of constipation. These symptoms are usually experienced once a week or more for at least four weeks. IMO also has a lot in common with IBS-C (constipation-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome).

What Causes ΙΜΟ

The causes of IBS and SIBO are pretty similar. They include medications and other GI conditions. More research is being done to figure out what causes IBS.

Which Gas Indicates IMO

Methane is produced when archaea consume hydrogen. If you have elevated levels of methane (CH4), as measured by a breath test, it’s likely you have IMO. A positive methane breath test is associated with constipation, and the level of methane measured correlates with the severity of constipation.

Excess Hydrogen Sulfide

Excess hydrogen sulfide is a condition that happens when there’s too much hydrogen sulfide-producing bacteria in the body. Before, it wasn’t possible to measure hydrogen sulfide to see if there was too much of it. But now, there are breath tests that can do that. Before, if someone had too much hydrogen sulfide, it wasn’t picked up on breath tests that only measured one or two gases.

Excess Hydrogen Sulfide Symptoms

Patients with high levels of hydrogen sulfide often share common symptoms with SIBO, including abdominal pain, bloating, gas, distension, flatulence, and especially diarrhea. Levels of hydrogen sulfide, as measured by a breath test, tend to correlate with the severity of diarrhea. These symptoms usually occur at least once a week for at least four weeks. Excess hydrogen sulfide has a lot in common with IBS-D (diarrhea-predominant irritable bowel syndrome) and IBS-M (mixed-diarrhea/constipation irritable bowel syndrome).

What Causes Excess Hydrogen Sulfide

It’s thought that excess hydrogen sulfide is caused when organisms in the gut consume hydrogen and produce hydrogen sulfide. Because measuring and capturing hydrogen sulfide is still a new process, further research is being done to find out what causes excess hydrogen sulfide and how to treat those who suffer from it.

Which Gas Indicates Excess Hydrogen Sulfide

Hydrogen sulfide (H2S) is produced when hydrogen sulfide-producing organisms consume hydrogen. If you have an elevated level of hydrogen sulfide, as measured by a breath test, it means you have too much. A positive hydrogen sulfide breath test means you’ll probably have more severe diarrhea, and the level of hydrogen sulfide measured correlates with the severity of diarrhea.

Person clutching their stomach in pain, depicting symptoms of digestive discomfort

Hydrogen, Methane and Hydrogen Sulfide Do Not Act Independently

Hydrogen (H2), methane (CH4), and hydrogen sulfide (H2S) interact in a complex way. Hydrogen is produced by fermenting bacteria, but it’s also consumed by other organisms, which results in the production of other gases, including methane and hydrogen sulfide.

There’s a balance-counterbalance effect between methane and hydrogen sulfide, which shows how microbes in the microbiome depend on each other biochemically. These findings are important because they show that measuring only one or two of the three main fermented gases isn’t enough.

Which Breath Test I Use

FoodMarble Aire 2 breath test device for measuring intestinal gases

FoodMarble Aire 2

In the past, I used the standard breath tests, which need to be repeated at least once at the beginning to diagnose SIBO/IMO and once after treatment to see the results. As the cost and the practicality of these tests didn’t work for my patients, I ended up using the FoodMarble Aire 2 exclusively.

The FoodMarble Aire 2 is a small, portable device that connects to your phone. You buy it once (it costs about the same as a breath test), and you can use it as many times as you want to instantly and easily measure the methane and hydrogen in your breath. I usually choose the 3-hour lactulose test with the Aire 2.

You can see more about how it works here: https://foodmarble.com/how-it-works-sibo-tracking/

If you want to get the FoodMarble Aire 2 with a 15-20% discount you can email info@panagiotistsintavis.gr with the subject FoodMarble and we’ll direct you or just click here.

SIBO Treatment

Array of foods high in FODMAPs potentially aggravating SIBO symptoms, including garlic, onions, and wheat products

If you’re looking to manage small intestinal bacterial overgrowth (SIBO), intestinal methanogen overgrowth (IMO), and excess hydrogen sulfide, it’s important to take a holistic approach that incorporates dietary changes, supplementation, and lifestyle modifications.


Low-FODMAP (preferred)

  • What it is: The low FODMAPs diet is all about cutting out foods that are high in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These include certain grains, vegetables, fruits, and dairy products.
  • Benefits: reduces fermentation in the intestine, reducing bloating and gas.

Specific carbohydrate diet (SCD) or the GAPS diet

  • What it is: These diets focus on removing complex carbohydrates, working similarly to the low-FODMAP diet by starving harmful bacteria in the small intestine.
  • Benefits: helps to reduce bacterial overgrowth.

Low sulfur diet (mainly for excessive H2S)

  • What it is: A diet with limited intake of high-sulphur foods. These include cruciferous vegetables, dairy products, eggs, garlic and onions.
  • Benefits: reduces the production of hydrogen sulfide.

Elemental diet

  • What it is: The elemental diet is all about simple nutrients, usually in powdered supplement form. They’re absorbed directly from the gut into the bloodstream, bypassing fermentation of microbes. This diet provides all the necessary nutrients in an easily absorbed form, minimizing the work the gut has to do.
  • Benefits: Highly effective in difficult cases of overgrowth and dysbiosis due to the limited residue, allowing the gut to rest and heal.


I don’t usually use antibiotics, but if you do, it’s best to get guidance from your doctor. The most common ones are:

  • Rifaximin: Particularly effective for SIBO, as it is not absorbed and acts locally in the gut without systemic effects.
  • Neomycin or metronidazole: often used in combination with Rifaximin and are particularly effective for the treatment of IMO.


  • Anti-microbial herbs: I often use herbal antimicrobials such as oregano oil, berberine and garlic extract or a combination of all of them like biocidin with very good results.
  • Peptic enzymes: Often necessary to help break down food and absorb nutrients. They help in relieving digestive discomfort.
  • Hydrochloric acid (HCl): HCl can help improve levels of acid in the stomach, which is vital for proper digestion and for preventing bacteria from entering the small intestine from the stomach. It therefore enhances protein digestion and reduces bacterial overgrowth by creating an acidic environment that is inhospitable to pathogenic bacteria.
  • Bile acids (ox bile): Particularly beneficial for people who have had their gallbladder removed or who suffer from bile acid deficiency. They help in the emulsification and breakdown of dietary fats and help regulate the flora of the small intestine.
  • Prokinetics: Necessary to maintain bowel motility after treatment with antibiotics or herbal antimicrobials to prevent recurrence of SIBO. They increase the function of the migratory motor complex (MMC), helping to remove food debris and bacteria from the gut. The best known herbal option is ginger.
  • Probiotics: The use of probiotics leads to controversial results and sometimes worsening of symptoms. It’s something I usually use after resolving microbial overgrowth with s. boulardii and soil-based probiotics being the first choice.
  • Omega-3 fatty acids and curcumin: Many times useful for reducing inflammation of the gut which is caused by and contributes to intestinal dysbiosis.
  • Glutamine: Necessary to improve the intestinal barrier and reduce the entry of microbes and food debris into the systemic circulation.

Lifestyle and Helpful Practices

  • Stimulation of the vagus nerve: Gargling and singing are 2 easy ways that can stimulate the vagus nerve, which plays a key role in controlling MMC and overall bowel motility. Another tool I commonly use is the Pulsetto (you can use the coupon panagiotis to get a special discount), a transcutaneous vagus nerve stimulation (tVNS) device.
  • Managing stress: Yoga, meditation, deep breathing and/or use of Pulsetto can improve vagus nerve and adrenal function and reduce stress, which negatively affects gut health and immune system health and motility.
  • Physical activity: Regular, moderate-intensity exercise can improve overall mobility and bowel health without putting undue stress on the body.
  • Quality sleep: Getting enough quality sleep helps regulate the body’s natural rhythms, supporting gut health and reducing stress and inflammation.


Illustration of a healthy gut with balanced microbiome, highlighting beneficial bacteria and a healthy intestinal lining

Small intestinal bacterial overgrowth (SIBO), intestinal methanogen overgrowth (IMO) and excess hydrogen sulphide are complex conditions that affect the gut microbiome, leading to symptoms like bloating, diarrhea, abdominal pain and malabsorption of nutrients.

The right treatment for each person must be tailored to their specific symptoms and medical history. It’s important to work with a trained healthcare professional to make sure the right steps are taken to ensure an effective yet safe treatment plan. Nutrition, supplement selection and use and lifestyle changes play a big part in managing symptoms and preventing relapse.

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