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- SIBO (Small Intestinal Bacterial Overgrowth) leads to an excessive number of bacteria in the small intestine, where they normally do not belong.
- These excess bacteria disrupt fat digestion by breaking down the necessary bile acids. As a result, fats cannot be properly emulsified and absorbed.
- The outcome is fatty stool (steatorrhea): pale, bulky, and foul-smelling stool that contains undigested fat.
- It is important to treat the underlying cause and prevent deficiencies (e.g., of fat-soluble vitamins).
Steatorrhea caused by SIBO
Content
1. SIBO
2. What is Steatorrhea?
2.1 How does fat digestion work?
3. How can SIBO lead to steatorrhea?
4. Other symptoms of SIBO
5. Diagnosis
5.1 Diagnosis of SIBO
5.2 Diagnosis of Steatorrhea
6. Therapeutic approaches
7. Conclusion
1. SIBO
SIBO is short for „Small Intestinal Bacterial Overgrowth“ 
and refers to a bacterial overgrowth of the small intestine. Under normal circumstances, most of the microorganisms in our gut reside in the large intestine , where they contribute significantly to digestion and support overall health. By contrast, the small intestine normally contains relatively few bacteria. However, when bacteria multiply excessively in the small intestine, the delicate balance of digestion can be disrupted. The bacteria begin processing nutrients at the site where the body is supposed to absorb them. This can lead to a range of symptoms, from bloating and abdominal pain to changes in stool. One of the possible symptoms is steatorrhea (1). Steatorrhea indicates that fat digestion is no longer functioning properly.
2. What is Steatorrhea?
Steatorrhea refers to stool that is unusually pale, bulky, foul-smelling, and often difficult to flush. The consistency may be greasy, and visible fat droplets can float in the water. Steatorrhea indicates that dietary fats are not being properly digested or absorbed.
2.1 How does fat digestion work?
Fat digestion in the small intestine occurs in several precisely coordinated steps. As soon as fat-containing food passes from the stomach into the small intestine, bile is released from the gallbladder. Bile contains bile acids, which act like a biological detergent and break the fat into tiny droplets. This process is called emulsification. At the same time, the pancreas releases fat-splitting enzymes, primarily lipase, into the small intestine. These enzymes break down the fat droplets, allowing them to be absorbed by the intestinal mucosa and transported into the body.
3. How can SIBO lead to steatorrhea?
In SIBO, the finely tuned process of fat digestion is disrupted by the excess bacteria in the small intestine. On one hand, the bacteria consume nutrients that are actually intended for the human host. On the other hand, their metabolic activity alters the pH in the small intestine, which can impair the function of digestive enzymes. Particularly problematic is that some of these bacteria chemically modify or break down bile acids (2). Once bile acids lose their original structure, they also lose their ability to effectively emulsify fats.
As a result, larger fat droplets remain in the chyme, making them less accessible to lipase. Additionally, bacterial metabolic products can irritate or inflame the intestinal mucosa. An inflamed mucosa has a reduced surface area for nutrient absorption and is no longer able to absorb fats and fat-soluble vitamins (A, D, E, and K) adequately. Consequently, larger amounts of undigested fat reach the colon, ultimately leading to the characteristic appearance of steatorrhea.
4. Other symptoms of SIBO
In addition to steatorrhea, individuals with SIBO often report bloating , abdominal pain , diarrhea or constipation . Furthermore, back pain, fatigue, changes in body weight, and nutrient deficiencies, as not only fats but also fat-soluble vitamins such as A, D, E, and K are absorbed less efficiently (3).
5. Diagnosis
5.1 Diagnosis of SIBO
The diagnosis of SIBO is usually made using a specialized breath test based on the measurement of hydrogen and methane levels. The test takes advantage of the fact that certain bacteria in the small intestine ferment sugars or other carbohydrates, producing gases that are subsequently exhaled through the lungs. For the examination, the patient first drinks a defined amount of a sugar solution, usually containing lactulose. or Glucose . If there is an excessive number of bacteria in the small intestine, they begin to break down the sugar shortly after ingestion. This produces measurable amounts of hydrogen or methane, which are determined at fixed intervals using a breath analyzer. Based on the timing and levels of the gases, the physician can identify, whether bacterial overgrowth is present and whether the bacteria are predominantly hydrogen-producing or methane producing which is important for therapy planning.
5.2 Diagnosis of Steatorrhea
The detection of steatorrhea is carried out using a so-called fecal fat test. This examination is designed to quantitatively assess the amount of undigested fat in the stool. Usually, a stool collection over several days is performed, often spanning a period of 72 hours. During this time, the patient carefully records the type and amount of fats consumed. The collected material is then analyzed in the laboratory to calculate the average daily fat content in the stool. In healthy individuals, this value is well below seven grams per day (4). Significantly higher values indicate a fat digestion or fat absorption disorder.
Anyone who repeatedly notices such changes (particularly bulky, shiny, foul-smelling stool that is difficult to flush) should not take it lightly. These symptoms can occur not only in SIBO but also in diseases of the pancreas, liver, or bile ducts. Therefore, timely medical evaluation is crucial to accurately determine the cause and enable targeted treatment.
6. Therapeutic approaches
The treatment of SIBO aims to reduce bacterial overgrowth and normalize intestinal function. Typically, specific antibiotics or antimicrobial herbal preparations are used. At the same time, a tailored diet can help relieve the digestive system. In cases of steatorrhea, it is important to address the underlying cause and, if necessary, supplement bile acids or digestive enzymes. Therapy should always be individualized and conducted under medical and/or nutritional guidance.
Appropriate treatment can not only alleviate digestive symptoms such as bloating, abdominal pain, and diarrhea but also prevent long-term nutrient deficiencies. In particular, the absorption of fat-soluble vitamins and essential fatty acids can be significantly impaired by disrupted fat digestion. Without treatment, the risk of subsequent health problems increases. Early intervention therefore not only addresses acute symptoms but also helps ensure long-term health.
7. Conclusion
Steatorrhea is not merely an annoying symptom but a serious warning sign from the body. It indicates that fat digestion and absorption are not functioning properly. In the context of SIBO, this often means that the excess bacteria in the small intestine disrupt the delicate process of fat breakdown and absorption. As a result, some dietary fats pass through the intestine undigested and remain visible in the stool. Anyone who repeatedly notices such changes in their stool should seek medical evaluation promptly. Targeted treatment can not only alleviate symptoms but also prevent long-term nutrient deficiencies.
8. FAQs
Can fatty stool always indicate SIBO?
No. Although SIBO can be a cause of fatty stools (steatorrhea), it is important to know that this can also be triggered by other conditions, such as those affecting the pancreas, liver, or bile ducts. Medical clarification is always necessary.
Which vitamins are particularly at risk of deficiency in fatty stools?
The fat-soluble vitamins are the most affected, as they require fat for absorption. These include vitamins A, D, E, and K. An untreated long-term fatty stool can lead to corresponding deficiency states.
How exactly do the bacteria in SIBO prevent fat digestion?
The excess bacteria in the small intestine break down or chemically alter bile acids. Bile acids act like a biological detergent that emulsifies (breaks down into tiny droplets) dietary fats. Without functioning bile acids, fats cannot be properly broken down by the enzymes and subsequently absorbed by the intestinal mucosa.
How does the SIBO breath test differ from the stool fat test?
The SIBO breath test measures gases (hydrogen and/or methane) in the breath after drinking a sugar solution to detect bacterial overgrowth. The stool fat determination (usually over 72 hours) measures the exact amount of undigested fat in the stool to confirm the presence of a fat digestion disorder.
How is fatty stool treated in SIBO?
The therapy primarily aims to eliminate SIBO through specific antibiotics or antimicrobial herbal preparations. Once the bacterial overgrowth is reduced, fat digestion almost always normalizes again. If necessary, bile acids or digestive enzymes can be added as support.
References
- Roszkowska P, Klimczak E, Ostrycharz E, Rączka A, Wojciechowska-Koszko I, Dybus A, Cheng YH, Yu YH, Mazgaj S, Hukowska-Szematowicz B. Small Intestinal Bacterial Overgrowth (SIBO) and Twelve Groups of Related Diseases-Current State of Knowledge. Biomedicines. 2024 May 7;12(5):1030. doi: 10.3390/biomedicines12051030. PMID: 38790992; PMCID: PMC11117733.
- Sellge, G., & Ockenga, J. (2024). Bakterielle Fehlbesiedlung des Dünndarms (SIBO)–Therapie, Ernährung, Mikrobiom. DMW-Deutsche Medizinische Wochenschrift, 149(18), 1071-1079.
- Wilhelmi, M., Studerus, D., Dolder, M., & Vavricka, S. (2018). SIBO:“small intestinal bacterial overgrowth”. In Swiss Med Forum (Vol. 18, No. 9, pp. 191-200)
- Azer SA, Sankararaman S.; Steatorrhea; 2023 May 16; In: StatPearls; Treasure Island (FL): StatPearls Publishing; 2025 Jan; PMID: 31082099
