Why SIBO comes back: the cleaning wave, underlying causes and prokinetics

Healthy state

The small intestine has its own cleaning crew. When you are fasting, the migrating motor complex Migrating motor complex A wave of muscle contractions that sweeps the stomach and small intestine empty about every one and a half to two hours when fasting. Eating interrupts it. More in the chapter “Intermittent fasting and meal timing: 16:8, 5:2 and Ramadan”, MMC for short, runs roughly every 90 to 120 minutes. It has three phases: a quiet phase, a phase of irregular contractions and finally a few minutes of strong, regular contractions that travel from the stomach to the end of the small intestine. This third phase is the actual cleaning wave.

The wave is controlled by the nervous system of the gut wall and by hormones, above all motilin, which is released in bursts from the duodenum while you are fasting. Every meal switches the pattern off and replaces it with digestive movements. The antibiotic erythromycin binds to the motilin receptor and can trigger a wave this way. That is why it is used at low doses to stimulate gut movement.

The wave is not the only protection. Stomach acid, bile, digestive enzymes, defences such as IgA IgA (secretory IgA) The antibody of the mucous membranes. It is released into the gut in large amounts, where it holds germs in the mucus without causing inflammation. More in the chapter “IgA: the antibody that keeps the gut clean, and what vitamin A, D and omega-3 have to do with it” and the valve to the large intestine also keep bacterial numbers in the upper small intestine low. If one of these mechanisms fails, the others partly compensate. If several fail, the risk of overgrowth rises considerably.

When people think of SIBO Small intestinal bacterial overgrowth (SIBO) Too many bacteria in the small intestine, where normally few live. Bloating and diarrhoea are typical; it is usually diagnosed with a breath test. More in the chapter “When the small intestine is too densely colonised”, they usually think of the bacteria. For lasting success, though, the more important question is why they were able to settle in the small intestine. The US society AGA therefore explicitly advises looking for causes and correcting them where possible, rather than only fighting the bacteria.

Disrupted state: causes and effects

Relapses are common. In an Italian study of 80 people whose breath test Breath test After drinking a sugar solution, hydrogen and methane in the breath are measured several times. This can reveal sugar intolerances and signs of bacterial overgrowth. More in the chapter “Gut tests: what they show and what they do not” was normal after one week of rifaximin, it was positive again in 13 percent after three months, 28 percent after six months and 44 percent after nine months. Overgrowth returned more often with older age, after removal of the appendix and with long-term use of acid blockers. Symptoms came back along with the positive test.

It is similar in IBS Irritable bowel syndrome Recurring abdominal pain linked to bowel movements, without tests finding another cause. Today it is understood as a disorder of gut–brain interaction. More in the chapter “The gut-brain axis” with diarrhoea: of 1074 people helped by a course of rifaximin, 64 percent had symptoms again within 18 weeks. A second course helped 38 percent, placebo Placebo A dummy treatment without an active ingredient. Comparing with it shows how much a remedy achieves beyond expectation and chance. 32 percent. Antibiotics relieve symptoms, but they rarely remove the cause.

A weak cleaning wave is one of the most important causes. In a measurement study, 68 people with IBS and an abnormal breath test had on average 0.7 cleaning waves in four fasting hours, compared with 2.2 in 30 healthy people. In those whose overgrowth had already been treated, movement was partly more normal again. What is cause and what is effect is not fully settled.

The wave weakens with nerve damage from long-standing diabetes, with opioids, with diseases of the gut muscle such as scleroderma and probably after severe gut infections. In rats, morphine stopped the cleaning wave and bacteria multiplied in the small intestine. An underactive thyroid also slows the gut: in small-bowel samples, 33 percent of people with hypothyroidism had overgrowth, compared with 15 percent without. In a large US database, the risk appeared lower in people treated with thyroid hormone. An older analysis of breath tests found the opposite, but the newer study is based on samples taken directly from the small intestine and is therefore more reliable.

Then there are causes no motility drug can fix: adhesions after abdominal surgery, narrowings such as in Crohn’s disease, pouches in the small intestine, blind loops after stomach or bowel surgery, and a removed or poorly closing valve to the large intestine. In a meta-analysis Meta-analysis An analysis that combines the results of several studies. It is only as good as the studies it includes. , acid blockers raised the risk by about 1.7 times. In a cross-sectional study from India, people taking a prokinetic Prokinetics Drugs that stimulate movement of the stomach and gut, such as prucalopride or low-dose erythromycin. alongside their acid blocker had SIBO less often than people on an acid blocker alone, 1.8 versus 13.2 percent.

Support groups and forums recommend many things for prevention: long breaks between meals, ginger, Iberogast, strict long-term diets, repeated herbal courses and prescription prokinetics. There is hardly any study evidence for them. The best studied are low-dose erythromycin and tegaserod, which was available at the time: in a retrospective analysis, people stayed symptom-free longer with them than without prevention. Tegaserod is no longer available in most countries.