What Is SIBO? Types, Symptoms, and Testing Decoded

Written By Rachel Carbone

by Rachel Carbone MS, BCDNM, LMT

When gut movement stalls, bacteria can shift into the small intestine, leading to Small Intestinal Bacterial Overgrowth (SIBO). Because your small intestine is not built to house large populations of fermenting microbes, it often triggers severe distention, gas, nausea, uncomfortable belly pressure, bowel fluctuations, and low energy (Cleveland Clinic, 2024).

The Different Types of SIBO

The specific symptoms you feel often depend on the type of gas your gut microbes produce (Min et al., 2024):

  • Hydrogen Dominant SIBO: Driven by hydrogen producing bacteria, often presenting as quick fermentation, loose stools, and sudden gas (Min et al., 2024).

  • Methane Dominant (IMO): Caused by archaea that convert hydrogen into methane gas. Methane actively slows gut movement, often leading to stubborn constipation and severe belly swelling (Min et al., 2024).

  • Hydrogen Sulfide SIBO: Often presents with sulfurous ("rotten egg") gas, loose stools, and sharp belly discomfort (Min et al., 2024).

  • Mixed Subtype: A combination of gases causing unpredictable shifts between loose stools, constipation, acid reflux, and fatigue (Min et al., 2024).

  • SIFO (Fungal Overgrowth): An overgrowth of yeast or fungus in the small intestine that can occur alongside or independent of bacterial overgrowth.

Why Gut Balance Matters

When bacterial overgrowth persists in the small intestine, it can irritate the delicate gut lining and interfere with how your body absorbs essential nutrients (Cleveland Clinic, 2024):

  • Vitamin B12 Depletion: Microbes can consume dietary B12 before your body gets a chance to absorb it (Cleveland Clinic, 2024).

  • Anemia Support: Poor absorption of iron and B12 linked to localized gut irritation (Cleveland Clinic, 2024).

  • Bone Density Support: Malabsorption of fats can reduce your body's uptake of fat soluble Vitamin D and calcium (Cleveland Clinic, 2024).

  • Kidney Stress: Unabsorbed fats bind calcium in the gut, leaving oxalates free to be filtered by the kidneys (Cleveland Clinic, 2024).

What Feeds the Overgrowth?

Bacteria in the small intestine thrive on simple, fast fermenting carbohydrates. Common trigger foods include refined sugars, sugar alcohols, high fructose fruits, starchy vegetables, unaged dairy, and wheat or grain fibers (Cleveland Clinic, 2024).

How SIBO Is Assessed

Standard stool tests only look at the large intestine. To evaluate what is happening higher up in the small intestine, specialized triple gas breath tests (like Trio Smart) are used to measure hydrogen, methane, and hydrogen sulfide levels over 3 hours.

  • Glucose vs. Lactulose Options: During a test, you drink a simple sugar solution. Glucose measures the upper small intestine, while prescription lactulose travels further down into the lower small intestine. Because humans cannot digest lactulose, it carries a higher chance of false positive results (~68% sensitivity and 44% specificity) (Peralta et al., 2009; Wang et al., 2021).

  • Spotting Methane Trends: Research shows a single baseline fasting methane score of 10 ppm or greater is 86.4% sensitive and 100% specific for identifying Intestinal Methanogen Overgrowth (IMO) without needing all 3 hours of testing (Takakura et al., 2022).

  • The Future of Gut Assessment: Emerging tools like the SIMBA capsule—a tiny ingestible capsule—sample fluid directly from the small intestine, offering detailed insights that differ fundamentally from stool samples (Wang et al., 2024).

Stop Playing the Testing Guessing Game

Choosing the right testing substrate, interpreting complex gas charts, and recognizing whether you are dealing with Hydrogen, Methane, or Hydrogen Sulfide patterns requires careful evaluation. As a holistic health coach, I help guide clients through functional testing protocols, taking the confusion out of your results so we can target your unique gut patterns naturally.

References

Cleveland Clinic. (2024, August 9). SIBO (small intestinal bacterial overgrowth). https://my.clevelandclinic.org/health/diseases/21820-small-intestinal-bacterial-overgrowth-sibo

Min, M., Nadora, D., Chakkalakal, M., Afzal, N., Subramanyam, C., Gahoonia, N., Pan, A., Thacker, S., Nong, Y., Chambers, C. J., & Sivamani, R. K. (2024). An Oral Botanical Supplement Improves Small Intestinal Bacterial Overgrowth (SIBO) and Facial Redness: Results of an Open-Label Clinical Study. Nutrients, 16. https://doi.org/10.3390/nu16183149

Peralta, S., Cottone, C., Doveri, T., Almasio, P., & Craxì, A. (2009). Small intestine bacterial overgrowth and irritable bowel syndrome-related symptoms: experience with Rifaximin. World Journal of Gastroenterology, 15, 2628–2631. https://doi.org/10.3748/wjg.15.2628

Takakura, W., Pimentel, M., Rao, S., Villanueva-Millán, M., Chang, C. Y., Morales, W., Sanchez, M., Torosyan, J., Rashid, M., Hosseini, A., Wang, J., Leite, G., Kowalewski, E., Mathur, R., & Rezaie, A. (2022). A Single Fasting Exhaled Methane Level Correlates With Fecal Methanogen Load, Clinical Symptoms and Accurately Detects Intestinal Methanogen Overgrowth. The American Journal of Gastroenterology, 117, 470–477. https://doi.org/10.14309/ajg.0000000000001607

Wang, B., Xu, Y., Hou, X., Li, J., Cai, Y., Hao, Y., Ouyang, Q., Wu, B., Sun, Z., Zhang, M., & Ban, Y. (2021). Small Intestinal Bacterial Overgrowth in Subclinical Hypothyroidism of Pregnant Women. Frontiers in Endocrinology, 12. https://doi.org/10.3389/fendo.2021.604070

Wang, G., Menon, S., Wilsack, L., Rehak, R., Lou, L., Turbide, C., Auger, J., Tremblay, A., Mathieu, O., Binda, S., Tompkins, T., Bruehlmann, S., & Andrews, C. N. (2024). Spatially and temporally precise microbiome profiling in the small intestine using the SIMBA capsule with X-ray tracking. Frontiers in Microbiomes, 3. https://doi.org/10.3389/frmbi.2024.1321624

Rachel Carbone
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Holistic SIBO Recovery: Nutrition, Herbals, and Motility