SIBO Symptoms
Quick answer: The core SIBO symptoms are bloating and abdominal distension (often worsening through the day and after carb-rich meals), excess gas, diarrhea or constipation, and sometimes nausea or fatigue. SIBO — small intestinal bacterial overgrowth — is when too many bacteria grow in the small intestine, where few normally live. Symptoms overlap heavily with IBS, so it’s diagnosed with a breath test, not guesswork.
SIBO has become a popular explanation for stubborn bloating — sometimes rightly, sometimes not. Because its symptoms look almost identical to IBS, it’s both under-recognized and over-diagnosed.
Here’s what small intestinal bacterial overgrowth actually is, and the symptoms that point to it.
The classic symptoms
The hallmark is bloating and visible distension that builds through the day and flares after meals rich in carbohydrates — the fuel the overgrown bacteria ferment. Add frequent gas and belching, altered bowel habits (diarrhea, constipation, or both), and sometimes nausea, cramping and fatigue.
In more significant cases, poor absorption of fat and vitamins (like B12) can occur. But for most people it’s the relentless post-meal bloat that stands out.
Why it's confused with IBS
SIBO and IBS share nearly the same symptom list, and a meaningful share of people diagnosed with IBS may have an element of SIBO. The difference is location: SIBO is specifically too many bacteria in the small intestine, where the population should be low. That’s why it can’t be diagnosed by symptoms alone.
Testing is usually a breath test measuring hydrogen and methane after a sugar drink — the gases the overgrown bacteria produce. It’s imperfect, which is one reason a clinician should interpret it.
Where the microbiome fits
SIBO is fundamentally a microbiome-distribution problem — the right bacteria in the wrong place, or too many of them. Management is medical (often antibiotics and addressing the underlying cause, like slow motility), and recurrence is common.
Diet and targeted gut support can play a role alongside medical care, but SIBO specifically warrants a clinician — this is one where self-treating with random probiotics can backfire. If bloating is relentless, get it properly assessed.
Find your pattern
Match, don’t guess. The free Gut-Brain Axis Assessment reads how your system behaves and points you to the matched GoodOnes formula.
References
- Pimentel M, Saad RJ, Long MD, Rao SSC. ACG clinical guideline: small intestinal bacterial overgrowth. Am J Gastroenterol. 2020;115(2):165–178.
- Ghoshal UC, Shukla R, Ghoshal U. Small intestinal bacterial overgrowth and irritable bowel syndrome: a bridge between functional organic dichotomy. Gut Liver. 2017;11(2):196–208.
- Cryan JF, O’Riordan KJ, Cowan CSM, et al. The microbiota–gut–brain axis. Physiol Rev. 2019;99(4):1877–2013.
This article is for education and does not diagnose, treat, cure, or prevent any disease. GoodOnes™ formulations support everyday gut function; they are not a substitute for medical care. If your symptoms are severe, persistent, or accompanied by warning signs, see a licensed clinician.
About the author
Craig Rouskey · CEO, Flore Inc. & Microbiome Scientist
MSc Molecular Biology, Microbiology, Biochemistry & Immunology (SIU). Craig is the scientist behind the GoodOnes™ targeted-probiotic line, built on a longitudinal dataset of 23,447 sequenced microbiomes. Former leadership at Renegade Bio, Pando Nutrition, and Bionascent; TEDxBellevue speaker on citizen science and precision health.