SIBO: small intestinal bacterial overgrowth, diagnosis and diet

Bloating that comes on in the minutes after a meal, a belly that swells from the first mouthfuls, discomfort that does not resemble “classic” dysbiosis: SIBO (Small Intestinal Bacterial Overgrowth) is a distinct entity, often confused, that requires a different protocol from colon-microbiome work.

SIBO: when bacteria move up into the small intestine

The small intestine is normally almost sterile: its bacterial density is a thousand times lower than the colon’s. SIBO is the proliferation of bacteria in the small intestine, where they should not be present in significant numbers.

The identified causes: a defect of the “cleansing wave” (the migrating motor complex that sweeps the small intestine between meals), hypochlorhydria (gastric acid is the first barrier), anatomical causes (adhesions, small-bowel diverticula), post-infectious causes (after gastroenteritis, post-infectious SIBO is documented), or drugs that slow transit.

The distinctive sign: immediate bloating, not delayed

SIBO differs from colon dysbiosis by its timing: bloating occurs during or immediately after the meal, not hours later. The reason is mechanical: small-intestinal bacteria meet the food bolus straight away and begin fermenting carbohydrates before absorption has occurred. In colon dysbiosis, fermentation waits for the bolus to reach the colon, hours later.

The associated picture: immediate bloating, often with early belching or flatulence, epigastric discomfort, sometimes a sensation of “food stagnating high up”. The associated deficiencies are characteristic: B12 (the bacteria consume it), iron, fat-soluble vitamins (the bacteria are thought to deconjugate bile salts).

Breath test and clinical signs

SIBO diagnosis rests on the breath test: the patient drinks a glucose or lactulose solution, and expired hydrogen and methane are measured over 2-3 hours. Early, excessive production signs SIBO. The test is imperfect (debated sensitivity and specificity, demanding preparation) but it is the tool available.

Clinical signs that point to it: immediate bloating, favourable response to specific antibiotics (rifaximin), aggravation by prebiotic fibres and high-FODMAP foods, unexplained B12 deficiency, a history of gastroenteritis or abdominal surgery.

The TCM reading: Spleen deficiency + stagnant Dampness

In TCM terms, SIBO is a picture of Spleen deficiency with Dampness stagnating in the Middle Burner. A Spleen that no longer transforms lets fluids stagnate; a small intestine that no longer separates the clear from the turbid lets ferment what should be absorbed. Immediate bloating is the signature of Dampness crowding the middle burner: the substance rises before being transformed.

The correspondence is remarkable: TCM described this picture as “Spleen deficiency with Dampness” (digestion that tires, bloating, variable stools) long before the breath test existed. What TCM adds: SIBO is not only an infection to treat, it is a terrain that permitted the infection, and it is that terrain that must be transformed.

The protocol: why prebiotics must wait

This is the essential difference from colon dysbiosis: in SIBO, the prebiotic fibres that feed the good colonic microbiome also feed the small-intestinal bacteria and worsen the picture. The classic SIBO protocol begins by reducing the fermentable substrate: a FODMAP-attenuation phase (the article on FODMAPs and Spleen Dampness details this protocol), often combined with treatment (a targeted antibiotic such as rifaximin, or an antimicrobial approach depending on the practitioner), then gradual reintroduction.

What differs from the dysbiosis protocol: during the acute phase one does not “feed” the microbiome; one “starves” it of its substrate. Prebiotics, inulin, pulses and certain FODMAP-rich vegetables are reduced, not because they are bad but because they feed the fire in the wrong place. Reintroduction comes afterwards, once cleansing has occurred.

Criterion	SIBO	Colon dysbiosis

FAQ: SIBO

What is the difference between SIBO and dysbiosis?

Dysbiosis is an imbalance of the colon microbiome (good and bad species deregulate); SIBO is a proliferation of bacteria in the small intestine, which is normally almost sterile. The distinctive sign: immediate bloating after the meal in SIBO, delayed in dysbiosis.

Is the breath test reliable?

It is the tool available, with limits: debated sensitivity and specificity, demanding preparation, possible false positives and negatives. It is interpreted with the clinical picture, not in isolation.

Why do prebiotics worsen SIBO?

Because they feed bacteria where they should not be: the small intestine. Fermentable fibre that would be good for the colon ferments in the small intestine before reaching it, producing the bloating. In SIBO, the acute phase reduces the substrate; reintroduction comes after treatment.

Can diet treat SIBO alone?

No: it manages the substrate and the terrain, but established bacterial overgrowth often requires treatment (rifaximin, an antimicrobial protocol depending on the practitioner). Diet is the condition of non-recurrence, not the eradication.

SIBO, the overgrowth that reveals itself through timing

SIBO is the most under-diagnosed cause of chronic bloating: a diagnosis that exists, a test that confirms it, a protocol that differs from colon dysbiosis. What distinguishes it is timing: a belly that swells during the meal, not hours afterwards. To locate your digestive terrain: the Yin Shi energy test maps your profile in a few minutes.