Functional Medicine · Hormonal Health

The Journal

by Dr. Natasha Ryan, ND

Gut Health · SIBO

SIBO in Women: Symptoms, Breath Testing, and What Treatment Looks Like

3 min read

If your stomach is flat in the morning and you look months pregnant by dinner, you've probably wondered about SIBO. Bloating that builds through the day is one of the classic patterns. But SIBO is also overdiagnosed online, and its symptoms overlap with several other conditions. Here's what it is and how to find out whether you have it.

What SIBO is

Small intestinal bacterial overgrowth means there are too many bacteria in the small intestine, which normally has relatively few. Most of your gut bacteria are supposed to live in the colon. When they build up higher in the digestive tract, they ferment food early, producing gas, bloating, and discomfort soon after you eat.

A related condition involves microbes that produce methane. Because these organisms aren't technically bacteria, the American College of Gastroenterology now calls it intestinal methanogen overgrowth, or IMO. Methane slows the gut, so IMO is more often linked with constipation.

Symptoms

According to the American College of Gastroenterology's 2020 guideline, bloating is the most prominent symptom. The most common are:

  • Bloating and visible abdominal distension
  • Gas and belching
  • Abdominal pain or discomfort
  • Diarrhea, or constipation when methane is involved

The guideline is clear that none of these is specific to SIBO. They overlap heavily with IBS and functional dyspepsia, which is why testing beats guessing.

Who's at risk

The guideline lists female sex and older age among the risk factors. Others include:

  • Long-term acid-suppressing medication such as PPIs
  • Slow gut motility, including from diabetes or opioid medications
  • Prior abdominal surgery
  • Celiac disease and some immune conditions

A slow-moving gut is the common thread. When things don't move through the small intestine efficiently, bacteria have time to accumulate.

How it's tested

SIBO is diagnosed with a breath test. You drink a sugar solution, either glucose or lactulose, and breathe into tubes every 15 to 20 minutes for two to three hours. Bacteria that ferment the sugar produce hydrogen or methane, which shows up in your breath.

The North American Consensus on breath testing defines the results this way:

  • Hydrogen: a rise of 20 ppm or more above baseline within 90 minutes suggests SIBO.
  • Methane: a level of 10 ppm or more at any point suggests methane overgrowth.

Preparation matters for an accurate result. The consensus recommends avoiding antibiotics for four weeks beforehand, eating a low-fermentation diet the day before, and fasting overnight. Your provider will give you the specific instructions.

How it's treated

Conventional treatment is antibiotics, most often rifaximin, which stays mostly in the gut. For methane overgrowth, combinations are often used. Herbal antimicrobial protocols are also widely used in functional medicine, though the research behind them is more limited.

The bigger issue is that SIBO comes back often. The guideline notes recurrence is common. That's why clearing the overgrowth is only half the job. The other half is finding out why it happened:

  • Is motility slow, and why? Thyroid function, blood sugar, and medications are worth checking.
  • Is stomach acid low from long-term acid blockers?
  • Is diet feeding the overgrowth? A short-term low-fermentation diet can ease symptoms during treatment.
  • Is stress affecting digestion? The nervous system has a direct effect on gut motility.

When it's not SIBO

If your breath test is negative, the bloating is still real. Other common causes include constipation, food intolerances like lactose or fructose, delayed food reactions, hormonal shifts across the cycle and through perimenopause, celiac disease, and pelvic floor problems. A good workup looks at all of them rather than stopping at one test.

References

  1. Pimentel M, et al. “ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth.” American Journal of Gastroenterology, 2020. View source
  2. Rezaie A, et al. “Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus.” American Journal of Gastroenterology, 2017. View source