Could SIBO be the cause of IBS?

by | Nov 11, 2023 | gut health and digestion

Irritable bowel syndrome or IBS is a very common condition of the gut. It often begins after a bout of food poisoning or other gut infection. People with IBS tend to have the condition long term and it can severely impact on their quality of life. Doctors used to believe that IBS was a psychosomatic condition. Sufferers were told there was nothing that could be done. But now in most cases, it appears likely that microbes in the gut could be a cause of IBS.

Our microbiome

Microbes are normal inhabitants of the intestines. Indeed there are many more microbes in the gut than there are human cells in the rest of the body. The trillions of bacteria on and in our bodies is called our microbiome. Most of our microbiome lives in the large intestine or colon. And they are crucial for our good health.

The intestines

The small intestine and the large intestine have different functions.

The small intestine is about 6 metres in length and occupies a large part of the abdomen. And most of the digestion and absorption of food occurs here. The material that is not absorbed passes into the large intestine.

In contrast, the large intestine is a shorter section of the gut, around 1.5 metres in length. This part of the intestine provides a home for trillions of bacteria. In turn, these bacteria provide useful nutrients such as short-chain fatty acids and some vitamins. Water is absorbed from the large intestine and then the remaining waste excreted.

The walls of the gut include muscle layers that can contract at intervals and push food along the gut. The rhythmic muscular waves continue between meals and serve to cleanse the bowel.

One theory suggests that gut infections such as gastroenteritis may damage the muscles of the gut. As a result, the damage may reduce the smooth motion or motility of the bowel.  Stress can also cause slowing or reduction of this wave. Whatever the cause of the slowed wave motion, there will be less clearance of material from the gut. And, bacteria that would otherwise remain in the colon may gain access to the small intestine.

Bacteria in the small intestine could then ferment food there. Producing gases which would result in bloating after meals. A typical symptom of IBS. These bacteria could also multiply in the food-rich environment of the small intestine. This is known as small intestine bacterial overgrowth or SIBO.

Pain and bloating are common symptoms experienced by almost all those with IBS. Other symptoms include constipation, diarrhoea or alternating between constipation and diarrhoea. If SIBO causes IBS how could the different symptoms be explained?

SIBO as a cause of IBS

Studies show that different types of gut microbes produce different gases. Typically hydrogen or methane. Some people with IBS have microbes that produce methane, and they develop constipation. And, those with microbes that produce hydrogen, predominantly have diarrhoea.

We also know that it is the methane that reduces the transit time of the colon. In other words the higher the production of methane, the slower the gut becomes. A slower gut results in constipation.

One of the major ways of testing for SIBO is to test for the presence of the gases hydrogen or methane. These gases can be detected using a breath test.

Finding the cause of IBS will aid in treatment options. Eating a diet low in FODMAPs as I discuss here can help to reduce symptoms of IBS. But a positive test for SIBO may need antimicrobial treatment. Some types of antibiotics can eliminate SIBO. Herbal medicines can also be used. Studies show these are just as effective or sometimes more effective for eliminating SIBO.

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