LAURA HAINEL

M.Sc. Clinical Nutrition

🕑 reading time: 3-5 Minuten

👆 Key facts in short

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• • In case of SIBO (Small Intestinal Bacterial Overgrowth) an excessive amount of bacteria lives in the small intestine, where they normally do not belong.
  • These excess bacteria can cause significant symptoms by y fermenting certain foods.
  • Symptoms such as bloating, abdominal distension, diarrhea, and also constipation are very common, depending on the type of overgrowth.

What is that and what symptoms are typical

Content
1. What is SIBO?
2. SIBO Symptoms
2.1 Abdominal Pain
2.2 Bloating
2.3 Diarrhea
2.4 Constipation
2.5 Further Symptoms
3. Types of SIBO
3.1 Hydrogen-SIBO
3.2 Methane-SIBO
3.3 Hydrogen-Sulfide-SIBO
4. SIBO Therapy and treatment

1. What is SIBO?

SIBO describes the pathological overgrowth of bacteria in the small intestine. In a healthy state, the small intestine—unlike the large intestine, whose gut flora is rich in bacteria—is only sparsely populated with bacteria. The amount of bacteria can be measured in colony-forming units (CFU). In the large intestine, there are about 10^10-10^12 CFU/ml, equating to 10 billion to one trillion bacteria. In contrast, the small intestine contains only 10^2-10^8 CFU/ml, with the bacterial count increasing as you move from the duodenum to the ileum.

The prevalence of SIBO is not well-established, but estimates range between 2.5% and 22%. Estimates suggest a global prevalence of 11%. There are multiple issues that can cause SIBO development.
The causes for the development of SIBO are varied. These include, for example, medications, impaired intestinal motility , reduced digestion , or an obstructed flow of food through the intestine. This bacterial overgrowth can lead to various complaints. Classic symptoms, in addition to abdominal pain , include bloating , nausea, and constipation .

2. SIBO Symptoms

Due to the increased bacterial growth in the wrong place (bacterial overgrowth), the small intestine is often overwhelmed. It cannot cope with the amount of gases and toxins produced by the bacteria. The consequences are digestive symptoms such as abdominal pain, bloating, changes in bowel movements such as diarrhea , constipation , belching, a feeling of fullness, and heartburn. The symptoms are often similar to those of irritable bowel syndrome. Some patients also complain of fatigue, difficulty concentrating, and depressive moods . Not all 11% of the world’s population are so severely affected that they require therapeutic support. In some cases, small intestinal bacterial overgrowth can also be completely asymptomatic.

The symptoms and complaints typically occur within the first 120 minutes after food intake and may be aggravated by a FODMAP-rich diet. FODMAPs (fermentable oligo-, di-, monosaccharides, and polyols) are fermentable carbohydrates that serve as food for bacteria. The foods in which they are found vary widely. They are often foods that are very high in fiber. These include cereals, dairy products, mushrooms, cabbage, and legumes. A special low-FODMAP diet can therefore often help alleviate symptoms.

An improvement of symptoms usually occurs after longer fasting periods. This is why complaints are often better in the morning and increase throughout the day as food intake progresses.

Let’s take a closer look at the individual symptoms:

2.1 Abdominal Pain

Abdominal pain is generally a warning signal for various gastrointestinal disorders. In addition to small intestinal bacterial overgrowth (SIBO), irritable bowel syndrome and visceral hypersensitivity should also be mentioned here. Because many bacteria settle in the small intestine in cases of SIBO—bacteria that normally do not occur there—abdominal pain can be one of the possible consequences. More information can be found in the article on abdominal pain in SIBO.

2.2 Bloating

A very common symptom of small intestinal bacterial overgrowth (SIBO) is abdominal bloating . Symptoms usually begin within the first 120 minutes after eating. Not all the time does this involve the passage of gas, and bloating may occur. The gas production takes place in the middle digestive tract. As a result, the gases may not be able to escape easily, which primarily leads to abdominal distension or increased belching. Another aspect is that people with irritable bowel syndrome are more sensitive to the amount of gas in the intestines. Thus, even a slightly increased amount of gas is more easily perceived.

2.3 Diarrhea

Small intestinal bacterial overgrowth (SIBO) has various consequences and symptoms. Due to the bacterial overgrowth, the intestine’s ability to absorb nutrients can be impaired. As a result, undigested food components may reach the large intestine, where they can draw water and lead to diarrhea . In addition, SIBO is often associated with impaired intestinal motility, which can also be a cause of diarrhea.

2.4 Constipation

In SIBO, not only diarrhea but also constipation can occur. This is primarily the case when the overgrowth is caused by archaea (methane-SIBO). Strictly speaking, archaea are not bacteria. Therefore, the term SIBO (bacterial overgrowth) is actually incorrect in this context. Nevertheless, this type of overgrowth is classified under SIBO.
Archaea produce the gas methane. This can slow intestinal transit time—that is, the time it takes for food or chyme to move through the intestine. This, in turn, promotes the development of constipation.

2.5 Further symptoms

Depending on where the overgrowth in the intestine is located, nausea or stomach discomfort may also occur. A leaky gut syndrome, meaning increased permeability of the intestinal lining, is also often observed in connection with SIBO. In some cases, weight gain or weight loss is reported. Thus, weight loss may, under certain circumstances, be associated with SIBO. This is often due to the fact that nutrients from food are not well absorbed as a result of changes in the intestinal microbiota. Other symptoms may also be visible on the skin . Acne, rosacea, and psoriasis/atopic dermatitis can be associated with SIBO. Some individuals with SIBO also face challenges at night . Bloating, abdominal pain, or restless leg syndrome can make nights restless. Dizziness and fatigue may also, in some cases, be indirectly related to SIBO.

3. Types of SIBO

There are three main types of SIBO, classified based on the primary gases produced by the bacteria: hydrogen (H2), methane (CH4), and hydrogen sulfide (H2S).

3.1 Hydrogen-SIBO

In hydrogen-dominant SIBO patients typically experience diarrhea , bloating , and flatulence. Hydrogen is a byproduct of various metabolic processes and is produced by numerous bacteria, including E. coli and Klebsiella. and flatulence. Hydrogen is a byproduct of various metabolic processes and is produced by numerous bacteria, including E. coli and Klebsiella.

3.2 Methane-SIBO

People with  Methane-dominant SIBO suffer mostly from  constipation bloating and belching. Methane is mainly produced by archaea. The term SIBO is therefore not entirely accurate here, since archaea are not bacteria. Methane-dominant SIBO is thus referred to as IMO (intestinal methanogen overgrowth) (3). In addition to the fact that archaea are not classical bacteria, they can overgrow both in the small intestine and in the large intestine. This is an important aspect when interpreting breath tests.Archaea and bacteria both belong to the prokaryotes, which means that unlike eukaryotes, they do not have a cell nucleus. Nevertheless, archaea and bacteria differ in their cell structure and metabolic processes.
The main causative agents of methane-dominant SIBO include Methanobrevibacter smithii (4), Methanomassiliicoccus, and Methanosphaera stadtmaniae.

3.3 Hydrogen-Sulfide-SIBO

In hydrogen sulfide SIBO , bacteria that produce hydrogen sulfide dominate. These include the Fusobacterium genus and Desulfovibrio species. Symptoms may include diarrhea, constipation, bloating (with a characteristic rotten egg smell), and brain fog.

Currently, there is no test in Germany to directly detect hydrogen sulfide in breath. Diagnosis is made through characteristic symptoms, as well as a lactulose breath test conducted over 180 minutes. Since lactulose can only be metabolized by bacteria, an increase in gas levels after 120 minutes indicates bacterial activity in the small intestine. If no increase is observed by 180 minutes, it suggests that hydrogen sulfide-producing bacteria have already metabolized the lactulose in the small intestine.

4. SIBO Therapy and treatment

SIBO treatment should be administered by a physician and typically involves specific diets , medication e.g. antibiotics (such as rifaximin) and probiotics. Diagnosis can be assisted by the SIBO breath test .

5. FAQs

References

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   3. Takakura W, Pimentel M. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome – An Update. Front Psychiatry. 2020 Jul 10;11:664. doi: 10.3389/fpsyt.2020.00664. PMID: 32754068; PMCID: PMC7366247.
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   6. Guo HZ, Dong WX, Zhang X, Zhu SW, Liu ZJ, Duan LP. [The diagnostic value of hydrogen sulfide breath test for small intestinal bacterial overgrowth]. Zhonghua Nei Ke Za Zhi. 2021 Apr 1;60(4):356-361. Chinese. doi: 10.3760/cma.j.cn112138-20200731-00725. PMID: 33765706.