Publicador de contenidos

Back to 20231005_OP_CIE_sibo

What is SIBO, the intestinal disorder popularized by social networks?


Published in

The Conversation

Ignacio López-Goñi

Member of the SEM (Spanish Society of Microbiology) and Full Professor of Microbiology, University of Navarra.

If you are Username a regular user of social networks, you have probably heard about the SIBO. From being hardly known to anyone, this intestinal disorder has become the talk of the town this summer, especially among young people and adolescents. Many influencers of Instagram and TikTok have shared that they were suffering its effects.

The story that repeats itself is the following: a person suffers from problems of heavy digestion, bloating and gas, heartburn, frequent diarrhea. They do a simple breath test and are told that they are releasing much more hydrogen than normal, due to an overgrowth of bacteria in the small intestine. You are prescribed antibiotics. As a result, the entire intestinal microbiota is altered and you are recommended to take probiotics to replenish it. Perhaps, by the way, you are offered a complete analysis of the intestinal microbiota from a sample stool sample. You get bored of taking probiotics, so they design a "personalized" per diem expenses . In the end, after several hundred (or thousands) of euros spent, you feel a little better... or not.

What does SIBO mean?

SIBO is not the name of a bacterium, it is the acronym for Small Intestinal Bacterial Overgrowth. We call intestinal microbiota the set of all microorganisms (bacteria, archaea, viruses, fungi and protozoa) that the digestive system harbors. It is made up of hundreds, probably thousands, of different species.

In reality, we are a complex ecosystem in balance with millions of interactions between these microbes and our cells. Microbiota support the healthy functioning of our digestive, immune, endocrine and nervous systems. It produces vitamins, short-chain fatty acids, amino acids, neurotransmitters, hormones and many other compounds.

When this balance is disturbed by changes in the composition or issue of microorganisms - known as dysbiosis - inflammatory bowel diseases, irritable bowel syndrome or metabolic disorders such as diabetes, obesity and allergies can develop.

But not everything is SIBO. Other types of gut microbiota disorders have been identified: LIBO (bacterial overgrowth in the large intestine), SIFO (fungal overgrowth in the small intestine) and IMO (intestinal methanogen overgrowth).

Too many bacteria in the small intestine

SIBO is the presence of colon-specific bacteria in the small intestine in amounts greater than 103 CFU/mL (Colony Forming Units per milliliter). This involves a change in the balance of individual species of microbiota in the small intestine and causes gastrointestinal symptoms. Patients with SIBO produce excess hydrogen due to fermentation of consumed carbohydrates.

Bacteria characteristic of this overgrowth include Streptococcus, Staphylococcus, Bacteroides and Lactobacillus. There is also usually an increase in the issue of microorganisms of the genera Escherichia, Klebsiella and Proteus.

In terms of symptoms, SIBO usually manifests with abdominal pain, bloating, gas, diarrhea and irregular bowel movements. These problems can lead to malabsorption, resulting in nutritional deficiencies, anemia or hypoproteinemia (decreased serum protein concentration).

In addition, the accumulation of microorganisms can generate an increase in some bacterial components (such as lipopolysaccharide) that stimulate an inflammatory response and generate chronic inflammation.

Diagnosis is made by aspirating the jejunal contents (endoscopically) and culturing sample at laboratory. A concentration greater than 103 CFU/mL in this culture would indicate the presence of SIBO. One of the limitations is that there is still no consensus on what is the normal microbiota in the small intestine.

Due to the invasive nature of this test, indirect breath tests are also used. They consist of measuring the amount of hydrogen and methane exhaled after drinking a mixture of water and glucose or lactulose. This subject of sugars is usually absorbed and degraded in the large intestine and not in the small intestine.

An increase of more than 20 ppm (parts per million) in hydrogen concentration compared to baseline is also used as a synonym for a diagnosis of SIBO. However, this test can give false negatives and false positives.

Is there an overdiagnosis of SIBO?

SIBO often accompanies diseases of the digestive system and other conditions. Bacterial overgrowth is more common in people with irritable bowel syndrome, Crohn's disease and other inflammatory bowel ailments. It has also been linked to celiac disease, fistulas, strictures, surgical procedures and obesity.

The prevalence is significantly higher among diabetic patients subject 1 and subject 2 than in the general population. Likewise, the coexistence of SIBO has been identified in nonalcoholic fatty liver disease, cirrhosis, chronic pancreatitis, cystic fibrosis, heart failure, hypothyroidism, Parkinson's disease, depression, systemic sclerosis and chronic renal failure.

In addition, irregularities in the structure and function of the intestinal wall, leave ileocecal valve pressure, excessive concentrations of some compounds, the presence of proinflammatory cytokines, and increased gastric pH can cause the disorder. In all these cases, there is an unresolved question: is it the overgrowth of bacteria in the small intestine that causes these diseases or is it these ailments that generate SIBO?

Changing our microbiota is much more difficult than we think.

Several strategies have been described to combat SIBO. Antibiotics are widely prescribed, although it is an empirical treatment, since it is initiated before information on the microorganisms involved is available. It is, therefore, a probability treatment. The evidence supporting its use is scarce and it can have other undesirable effects on the intestinal microbiota, favoring the development of resistance or infection by Clostridioides difficile.

A temporary beneficial effect has been suggested by reducing fermentable foods in the per diem expenses and avoiding products rich in fiber, polyols, sweeteners and prebiotics. These are called low FODMAP diets (fermentable oligosaccharides, disaccharides, monosaccharides and polyols). They are based on temporarily reducing certain foods (sugars, starches and fiber) that are poorly assimilated in the small intestine, absorb a lot of water - which alters peristaltic movements - and ferment rapidly in the colon, producing a lot of gas.

There is very little quality research on the effect of probiotics on the small intestinal microbiota and, in particular, for the treatment of SIBO. The status is similar with fecal microbiota transplantation: there is insufficient evidence to justify its efficacy.

It should also be noted that a person can test positive for SIBO and be perfectly healthy with no symptoms. All these treatments do not "cure" SIBO, they can only temporarily alleviate the symptoms. SIBO is not a disease, it is a symptom. To eradicate it you would have to go to the causes, and the increase of issue of bacteria is probably a side effect of other diseases that are the ones to be treated.


Although there is an extensive bibliography on SIBO and the other intestinal dysbioses, its quality is generally limited. Despite recent interest in the gut microbiome and its disorders, more clinical research is needed to determine the pathophysiology, identify effective treatments, and prevent microbiota overgrowth in the small and large intestine.

It is not only necessary to know who is there (metagenomics) but to know what they do and what functions they have (metatranscriptomics and metaproteomics). Future research may allow us to use specific changes in the composition and diversity of the intestinal microbiota as biomarkers of health or specific diseases. For the time being, the most urgent issue is perhaps to reach a consensus on protocols. And in case of doubt, always seek medical advice and do not self-diagnose or self-medicate.

This article was originally published in The Conversation. Read the original.

The Conversation