If you have been told you have IBS in India, there is a meaningful chance the actual problem is small intestinal bacterial overgrowth, and there is a near-certain chance nobody has tested you for it. SIBO is one of the most under-diagnosed gut conditions in Indian clinical practice. The test is widely available, the treatment is straightforward, and the difference between catching it and missing it can be five years of your life. This is the careful read on what it is, how to recognise it, and why the standard IBS workup almost always misses it.
What SIBO actually is
The small intestine is supposed to be relatively low in bacteria. Most of your gut microbiome lives in the colon, where it belongs. SIBO, small intestinal bacterial overgrowth, is when bacteria proliferate in the small intestine in numbers they should not. The bacteria are not necessarily pathogenic. They are just in the wrong room.
The wrong-room problem matters because the small intestine is where most digestion and absorption happen. When bacteria are present in numbers, they ferment carbohydrates before the small intestine can absorb them. The fermentation produces gas. The gas distends the small intestine. The patient bloats, often dramatically, often by evening. Carbohydrates and fibres make it worse. The familiar IBS picture appears.
In our clinic, about a third of patients who arrive with an IBS label have SIBO that has never been tested for. After the breath test confirms it, the treatment plan changes completely. The probiotic that was making things worse gets stopped. The targeted antimicrobial that addresses the overgrowth gets started. The motility drugs get added if the migrating motor complex needs support. Within four to eight weeks, the symptom picture transforms.
How SIBO actually presents
The classic SIBO patient has a few telltale features. Not all of them, but usually three or four.
Bloating that gets worse through the day. The patient wakes up with a flat abdomen. By lunch, the waistband is uncomfortable. By dinner, the stomach is visibly distended. By bedtime, the patient looks pregnant. This pattern is not subtle once you know to ask about it.
Bloating triggered by carbohydrates and certain fibres. Especially fermentable carbohydrates: onions, garlic, beans, lentils, certain fruits, sweetened drinks, wheat. The patient often has a long list of foods that make things worse, but cannot find a consistent pattern.
Alternating bowels or chronic constipation. Methane-dominant SIBO produces constipation. Hydrogen-dominant SIBO produces alternating or loose stools. Both qualify as "IBS" under the standard label.
Reflux, often without obvious cause. The pressure from the small-bowel distension pushes upward. PPIs help temporarily but do not address the underlying pressure.
Brain fog after meals. Bacterial overgrowth can produce neurotoxic byproducts that affect cognition.
Weight that will not shift, or weight loss that cannot be explained. Both happen. SIBO disrupts nutrient absorption, sometimes producing weight loss in patients who are eating adequately. Methane SIBO, paradoxically, often produces weight gain because the methanogens slow gut motility.
A history of food poisoning, gastroenteritis, or repeated antibiotic courses. These are common predisposing events.
Worsening after probiotics. The single most useful diagnostic clue. If a generic probiotic made you worse, SIBO is high on the list.
If you recognise three or four of these in your own picture, please ask for a breath test.
The breath test, properly done
The lactulose breath test is the standard SIBO test in India. It involves drinking a measured dose of lactulose and breathing into a bag at fifteen-minute intervals over three hours. The breath samples are analysed for hydrogen and methane. A rise above defined thresholds at specific time points is diagnostic for SIBO.
The test is widely available in major Indian cities through specialty diagnostic centres. It costs around 4,000-7,000 rupees depending on the lab. It is well-tolerated.
There are some technical points worth knowing.
The prep matters. Twenty-four hours of low-fermentable food before the test. No probiotics, prebiotics, or fibre supplements for two weeks. No antibiotics or antifungals for four weeks. The lab will give specific instructions.
The timing matters. Three hours, with samples every fifteen minutes. Some labs run shorter protocols. Insist on the full three hours.
Both hydrogen and methane should be measured. Some labs measure only hydrogen. Methane-dominant SIBO will be missed. Insist on both.
The cut-offs and timing of the rise determine the diagnosis. A rise of 20 ppm of hydrogen above baseline within 90 minutes, or any methane above 10 ppm at any point, is broadly considered diagnostic. The interpretation is more nuanced than this and your doctor should walk through the actual graph with you.
If your last gut workup did not include a breath test and you have the symptoms above, please ask.
The breath test is widely available, well-tolerated, and changes the plan more than any other gut test we run.
Hydrogen vs methane vs hydrogen sulfide
There are three subtypes of SIBO and they behave differently. The distinction matters because the treatment differs.
Hydrogen-dominant SIBO is the most common. Produced by hydrogen-producing bacteria. Tends to cause loose stools, bloating, and the more dramatic gas symptoms. Usually responds to a 14-day course of rifaximin (Xifaxan) or to herbal antimicrobials like berberine, oregano oil, and neem.
Methane-dominant SIBO (technically called intestinal methanogen overgrowth, IMO, since methanogens are archaea, not bacteria) is the trickier subtype. Produced by methanogens, which live alongside hydrogen-producing bacteria and feed on the hydrogen they produce. Methane slows gut motility, so methane SIBO classically presents with constipation. Treatment usually requires combination therapy: rifaximin plus neomycin, or rifaximin plus metronidazole, often for longer courses. Methane SIBO is more recurrence-prone.
Hydrogen sulfide SIBO is the newest recognised subtype. Produces classic SIBO symptoms with a notable sulphur-smelling gas profile. Standard breath tests do not measure hydrogen sulfide directly, so the diagnosis is inferential. Treatment overlaps with hydrogen-dominant approaches.
The treatment plan looks different for each subtype. This is one of the major reasons we run the test rather than empirically treating: the plan depends on what we are treating.
What we do after a positive test
A typical SIBO treatment course in our clinic runs roughly as follows.
Phase 1: kill, 4-6 weeks. Either pharmaceutical antimicrobials (rifaximin alone for hydrogen-dominant, rifaximin plus neomycin for methane-dominant), or herbal protocols using combinations of berberine, oregano oil, neem, allicin, and others. Pharmaceutical and herbal approaches both work; the decision depends on patient preference, severity, and tolerance.
Phase 2: motility support. Migrating motor complex support is critical. The MMC is the wave of contractions that clears the small intestine between meals. SIBO patients usually have suppressed MMC function. Prokinetics (low-dose erythromycin, or low-dose naltrexone, or ginger preparations) are used to support it. Eating windows are restructured to give the MMC space to work: no snacking between meals, longer overnight fast.
Phase 3: rebuild, 4-8 weeks. Once the overgrowth is treated, we rebuild the microbiome. Specific probiotic strains chosen to match the post-treatment picture (not generic broad-spectrum). Prebiotic fibres reintroduced gradually. Fermented foods added back where tolerated.
Phase 4: maintenance. The eating window stays. The motility support tapers. We retest at month six and month twelve to catch recurrence before it becomes severe.
About 60% of patients clear SIBO with one round of treatment. Methane patients often need two or three rounds. Recurrence within twelve months is around 30%. The maintenance pattern reduces but does not eliminate recurrence.
What recovery looks like
Bloating usually starts to ease within two weeks of starting antimicrobials. Most patients see dramatic symptom improvement by week six.
Bowels regularise as the overgrowth resolves and the motility support kicks in.
Energy and brain fog tend to improve in the second month, after the bacterial byproducts clear and absorption improves.
Skin and mood follow the gut, often by month three or four.
Weight begins to move once absorption normalises, in either direction depending on baseline.
The longer gut pillar piece gives the broader gut-everything frame, and the chronic urticaria post shows what happens when SIBO is the unrecognised driver behind a stubborn skin condition.
