What is SIBO?
Small Intestine Bacterial Overgrowth (SIBO) is a clinical condition characterised by an overgrowth of bacteria in the small intestine, which disrupts the normal microbial balance in this part of the gut and can lead to a range of digestive problems.
The small intestine normally contains a low amount of bacteria compared to the large intestine. In SIBO, excess bacteria interfere with normal digestion and absorption of nutrients.
What can cause SIBO?
SIBO is often associated with factors that interfere with intestinal motility or the gut’s natural defence against bacterial growth. Common causes include:
- Intestinal motility disorders:
- Irritable Bowel Syndrome (IBS): disturbances of normal bowel movement may contribute to bacterial growth.
- Gastroparesis: delay in gastric emptying, which may facilitate bacterial growth.
- Scleroderma or diseases affecting the musculature of the digestive tract.
- Anatomical alterations:
- Abdominal surgery.
- Diverticula in the small intestine: small sacs that can accumulate bacteria.
- Immune deficiencies (such as HIV or the use of immunosuppressive drugs) can impair the gut’s natural defence against bacterial infections.
- Inflammatory bowel disease: conditions such as Crohn’s disease can alter the integrity and function of the small intestine, facilitating abnormal bacterial growth.
- Ageing: with the passage of time, intestinal motility tends to decrease, which may predispose older people to SIBO.
- Recurrent use of antibiotics: although antibiotics may temporarily reduce bacterial overgrowth, prolonged or repeated use may alter the normal intestinal microbiota.
Symptoms of SIBO
Symptoms of SIBO vary in severity and mainly include digestive complaints. These symptoms can be similar to other gastrointestinal disorders, which sometimes makes diagnosis difficult. The most common symptoms include:
- Abdominal distension: feeling of bloating or increased abdominal volume, especially after eating.
- Flatulence: excessive production of intestinal gas, often with a bad odour.
- Abdominal pain or discomfort: cramping or widespread pain in the abdomen, which may worsen after eating.
- Diarrhoea: frequent watery stools, sometimes with a foul smell, due to bacterial fermentation of undigested carbohydrates.
- Constipation: although less common, some people with SIBO suffer from constipation.
- Malodorous or greasy stools (steatorrhea): difficulty in digesting and absorbing fats, resulting in undigested fats in the stool.
Moreover, due to interference with the absorption of essential nutrients, SIBO can also lead to symptoms of nutritional deficiencies:
- Unexplained weight loss: occurs due to malabsorption of nutrients.
- Fatigue: poor absorption of nutrients, especially vitamins B12, A, D, E and K, can cause chronic fatigue.
- Vitamin B12 deficiency: bacterial overgrowth can interfere with vitamin B12 absorption, resulting in megaloblastic anaemia and neurological symptoms (tingling, weakness, balance problems).
- Bloating or oedema: protein deficiency can cause fluid retention.
How is SIBO diagnosed?
As already mentioned, the diagnosis of SIBO can be challenging because its symptoms are similar to those of other gastrointestinal disorders, such as irritable bowel syndrome (IBS) or food intolerance. A series of tests and clinical procedures are used to diagnose it, of which we will examine the two main ones.
On the one hand, the most commonly used test to diagnose SIBO is the breath test. It is based on the measurement of gases (hydrogen and methane) produced by bacteria fermenting carbohydrates in the small intestine. The patient ingests a lactulose or glucose solution and then the level of these gases in the breath is measured at regular intervals. An early increase in hydrogen or methane production indicates the presence of bacteria in the small intestine.
There is another, more accurate method for diagnosing SIBO, but it is invasive and complicated to perform: aspiration and culture of the contents of the small intestine. This involves taking a sample of fluid from the small intestine by endoscopy and culturing it in the laboratory to quantify the number of bacteria present. A count of more than 10^3 colony-forming units per millilitre (CFU/ml) in the small intestine is considered diagnostic of SIBO.
Its relationship with other diseases
SIBO does not usually occur in isolation, but is associated with a number of underlying diseases that may contribute to its development or are aggravated by bacterial overgrowth. Some of these diseases include:
- Irritable Bowel Syndrome (IBS): there is a strong correlation between SIBO and IBS. It is estimated that 30-85% of IBS patients have SIBO. Altered intestinal motility in IBS may facilitate abnormal bacterial growth in the small intestine.
- Connective tissue diseases such as scleroderma: scleroderma and other autoimmune diseases affecting the connective tissue can cause dysfunction in the musculature of the digestive tract, resulting in reduced intestinal motility and promoting SIBO.
- Untreated coeliac disease: people with poorly controlled coeliac disease have a higher risk of developing SIBO due to damage to the intestinal mucosa and malabsorption.
- Crohn’s disease: this inflammatory bowel disease can affect any part of the digestive system; when it affects the small intestine, it can cause strictures (narrowing) or areas of dysfunction that favour bacterial growth.
- Short bowel syndrome or small bowel surgery: people who have undergone small bowel resections or bariatric surgery (such as gastric bypass) have reduced or altered intestinal motility, which favours the development of SIBO.
- Immune system diseases: immune deficiencies (such as HIV/AIDS or the use of immunosuppressants) can compromise the body’s defences against bacterial infections, facilitating the development of SIBO.
- Hypothyroidism: a decrease in thyroid function can slow down intestinal motility, favouring bacterial growth.
Treatments for SIBO
The treatment of SIBO aims to reduce the number of bacteria in the small intestine, improve digestion and prevent bacterial growth from reappearing. Since SIBO can have several causes and manifestations, any treatment must be individualised and supervised by a physician. The most common approaches to treating SIBO are described below:
Antibiotics
One of the main treatments for SIBO symptoms is the use of antibiotics to reduce the excess of bacteria in the small intestine. Among the most widely used is rifaximin, a broad-spectrum antibiotic that acts locally in the gut without being absorbed in large quantities by the body, minimising side effects. In cases where methane-producing bacteria are involved, rifaximin can be combined with neomycin.
However, it is crucial to remember that antibiotics should only be prescribed by doctors, as inappropriate or excessive use of antibiotics can lead to bacterial resistance, making it difficult to treat future infections. Doctors are the trained professionals to determine when antibiotics are needed, the appropriate dosage and duration of treatment, taking into account the individual characteristics of each patient. In addition, overuse of antibiotics can affect the body’s natural bacterial flora, weakening the immune system and potentially worsening the symptoms of SIBO.
Dietary changes
Dietary changes are key to alleviating the symptoms of SIBO and reducing the bacterial fermentation that occurs in the small intestine. One of the most commonly recommended dietary strategies is to follow a low FODMAP diet, which reduces the intake of certain types of carbohydrates that ferment easily in the gut, causing gas and bloating. In some severe cases, doctors may recommend an elemental diet, which consists of a liquid formula of predigested nutrients.
Probiotics and supplements
The use of probiotics in the treatment of SIBO remains a matter of debate. While some studies suggest that some probiotics may help restore the balance of intestinal flora, others point out that in some cases they may worsen symptoms by increasing the number of bacteria in the small intestine. In any case, if used, it is essential to select specific probiotic strains and under the guidance of a healthcare professional.
Treatment of underlying causes
It is crucial to identify and treat any underlying medical condition that may contribute to the development of SIBO. For example, in patients with hypothyroidism, adjustment of hormone treatment can improve bowel function and prevent SIBO recurrences.
Furthermore, in patients who have been using proton pump inhibitors (PPIs), such as omeprazole, for a long time to control heartburn, it may be useful to assess the need for continued treatment, as these drugs can reduce gastric acidity by facilitating bacterial growth in the small intestine.
Recognising the symptoms of SIBO – the first step
If you have symptoms such as bloating, flatulence, diarrhoea or persistent abdominal pain, you may have SIBO. Recognising the symptoms of SIBO is the first step in seeking treatment and improving your quality of life. With a correct diagnosis and customised treatment, you can control your symptoms and prevent SIBO from becoming a recurring problem. If you suspect that you have SIBO, consult a specialised physician to get the right treatment.
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