What is SIBO?
SIBO (small intestinal bacterial overgrowth) is a state in which bacteria that should mostly live in the large intestine overgrow into the small intestine. The small bowel is meant to stay low in bacterial density. When microbes ferment food there first, they produce bloating, gas, frequent flatulence, abdominal pain, diarrhea or constipation, and impaired nutrient absorption.
What are the main symptoms?
Post-meal bloating and gas, frequent foul-smelling flatulence, abdominal pain, and altered bowel habits (diarrhea, constipation, or alternating) are the most common. Alongside them, many people have bad breath, brain fog and anxiety, chronic fatigue, appetite and weight-control problems, and skin issues — because the gases and metabolites made in the small bowel do not stay in the gut; they reach the whole body.
What causes SIBO?
Structural causes exist — slow motility, low stomach acid, an impaired ileocecal valve — but the factor most often missed in clinic is diet. Fiber, whole grains, sulfur-rich vegetables like garlic and onion, fermented foods, and probiotics are widely recommended as healthy, yet when they are not fully absorbed in the small bowel they become fermentation substrate — food for the bacteria. The foods people are taught are "good for you" can paradoxically feed the overgrowth.
No single diet is "the cause." It is the combination of poorly-absorbed substrate + sulfur lingering in the small bowel that drives the overgrowth forward.
How is SIBO tested?
The standard test is a breath test measuring exhaled hydrogen and methane over time after drinking glucose or lactulose. The catch: standard panels often leave out hydrogen sulfide (H₂S) and methyl mercaptan (CH₃SH) — so an overgrowth accompanied by a foul odor can be misread as "normal."
If a real smell is present (noticed by you or by others), a normal hydrogen/methane result does not rule out sulfur-gas overgrowth.
How is SIBO treated?
Treatment usually pairs antibiotics that reduce the overgrown bacteria with a diet that lowers fermentation substrate. A low-substrate pattern built on refined white rice, minimizing fiber, garlic, onion, and fermented foods, often helps.
Specific drugs, doses, and duration differ by individual and must be decided through medical care. This page describes a general approach; it does not provide a prescription.
Why does it keep coming back?
Even after treatment lowers the bacterial count, returning to a diet centered on fiber, whole grains, fermented foods, and probiotics feeds the bacteria again, making relapse likely. Continuing probiotics on the belief that you are "adding good bacteria" can actually bring relapse sooner.
Do probiotics help?
Contrary to common belief, adding external bacteria (probiotics) to a small intestine that is already overgrown can make things worse. Probiotics are recommended on the premise of replenishing beneficial flora in the large intestine, but SIBO is not a "too few bacteria" state — it is a "too many, in a place they should not be" state.
For eight years, what was measured was not the smell — it was the number.
A clinical frame that confirms SIBO with breath-gas readings, not impressions.
8 years in clinic
Time spent directly measuring breath gases in patients with SIBO, delayed food sensitivity, and dermatitis at a clinic in Gangnam, Seoul.
Includes H₂S · CH₃SH
Measuring hydrogen sulfide and methyl mercaptan — the gases standard panels miss — so odor-accompanied overgrowth is not overlooked.
The Carnirice approach
Refined carbohydrate (white rice) + simple protein, minimizing alliums, cruciferous vegetables, and fermented foods. A clinical form of the low-substrate diet.
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The English-language writing on SIBO, sulfur-reducing bacteria, GLP-1, and the gut–skin axis lives on Substack.
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