Did You Know There is More Than One Type of SIBO Test on the Market?

The answer might surprise you...

Welcome to the Gut Honest Truth blog where a Certified Functional Medicine Practitioner gives you digestible information to tackle your chronic health concerns.

That's me, Katie Morra; and in this blog I'm going to break down the three types of SIBO, why the distinction matters for treatment, and how to make sure you're being tested correctly.

Side note — If you want an even deeper dive into understanding and resolving SIBO, check out my How to Get Rid of Your SIBO e-book..

And as always, working one-on-one for your specific needs is always our top recommendation, check out our appointment options to get started with one of our licensed health care professionals today.

SIBO: The Queen of IBS

SIBO stands for Small Intestinal Bacterial Overgrowth — and it's responsible for up to 80% of all IBS cases. I like to think of it as a party happening on the rooftop when it should be in the basement.

The small intestine should maintain very low bacterial counts. The large intestine — what most people picture when they think of the "microbiome" — is where trillions of bacteria belong. When bacteria overgrow in the small intestine, it directly impairs your ability to digest and absorb food, leading to a cascade of nutrient deficiencies and downstream health consequences.

What Does the Small Intestine Actually Do?

The small intestine is a muscular, open tube extending from your stomach to your large intestine (colon), made up of three sections: the duodenum, jejunum, and ileum. Its primary job is to digest food and absorb the energy and nutrients you need to function. It also:

• Produces hormones that stimulate the release of bile and pancreatic fluids

• Is the primary site of peristalsis — the wave-like contractions that move food, bacteria, and debris through your digestive tract

When bacterial overgrowth disrupts this organ, everything downstream is affected — including hormone balance, thyroid function, skin health, and more.

The 3 Types of SIBO

This matters — because each type requires a different treatment approach. Getting diagnosed with "SIBO" without knowing which type is like getting a flat tire and not knowing which wheel.

Hydrogen SIBO (H2)

Caused by an overgrowth of bacteria — including klebsiella, E. coli, proteus, or aeromonas — hydrogen SIBO is associated with IBS-Diarrhea. One important detail: hydrogen gas can serve as a food source for the other types of SIBO. If you have combination SIBO (hydrogen and methane together), you must address both — otherwise the methane producers will keep getting fed and the overgrowth won't clear.

Methane SIBO (CH4)

Technically produced by an archaea rather than a bacteria, methane SIBO is associated with IBS-Constipation. Methane-producing organisms are remarkably efficient at extracting calories from food — which is why people with methane SIBO often experience weight gain or an inability to lose weight despite a clean diet. It's also generally more challenging to treat than hydrogen SIBO alone.

Hydrogen Sulfide SIBO (HS)

The hallmark of hydrogen sulfide SIBO is sulfurous, rotten-egg-smelling gas. Patients with this type often experience loose stool, but also brain fog, memory issues, fatigue, muscle pain, and alternating diarrhea and constipation. Hydrogen sulfide-producing bacteria compete with methane producers for hydrogen gas — making this a particularly complex type to treat. It often develops when sulfur metabolism is impaired and the body compensates by growing more hydrogen sulfide-producing bacteria.

The 3 SIBO Tests Currently Available

Each test involves drinking a glucose or lactulose solution, then breathing into collection tubes over 2-3 hours to capture the gases produced by bacteria in your intestinal tract.

Glucose Test

Detects SIBO only in the upper (proximal) portion of the small intestine. Since most SIBO cases occur further down (distally, near the large intestine), false negatives are more common with this test. That said, a positive result is more likely to be a true positive. Best suited for patients whose symptoms begin within an hour of eating.

Lactulose Test

More likely to detect SIBO since the solution isn't absorbed by the small intestine — meaning it travels further and can detect more distal overgrowth. However, it has a higher rate of false positives since the solution can reach the large intestine and generate a response there. This is where clinical judgment matters — a practitioner needs to interpret the full picture, not just the number. It's the most commonly ordered test for good reason.

Trio-Smart Test

Released in 2020 and the first test capable of detecting all three types — hydrogen, methane, and hydrogen sulfide. Available in both glucose and lactulose options. Since hydrogen sulfide SIBO couldn't be tested before this, research on treatment is still developing — but this test has been a meaningful advancement in SIBO diagnosis. Can only be ordered by a physician.

No test is perfect. But knowing your type — and where the bacteria is located — is critical to knowing how to treat it.

Testing Tips

1. Get the at-home mail-in test — in-office SIBO tests are often shorter and less accurate

2. Always choose the 3-hour test over the 2-hour option

3. SIBO cannot be diagnosed by stool test — if a provider told you that you have SIBO based on a stool test, it's worth getting a second opinion

4. Stop antimicrobials and probiotics 2-4 weeks before testing — 4 weeks after any antibiotics

5. Avoid vitamin C, magnesium, ginger, and laxative supplements for at least 4 days prior

6. Follow the prep diet for 24 hours before — clear broths, lean meats, white rice only; no fiber, lactose, or spices

7. Fast for 12 hours before the test — if you stop eating at 8pm, begin the test no earlier than 8am

8. No exercise or smoking before testing

9. Drink the solution that comes in the kit — this sounds obvious, but you'd be surprised

The Connection Between SIBO and Everything Else

SIBO rarely exists in isolation. The most common underlying drivers include low stomach acid, chronic stress, slowed motility (often from hypothyroidism), H. pylori, adhesions, foodborne illness, and medications including PPIs and antibiotics.

This is why treating SIBO without addressing the root contributors often leads to relapse. At GHT we use both a GI-MAP stool test and SIBO breath testing together to get the full picture — large intestine and small intestine — before building a protocol.

If you're a practitioner wanting to learn more about functional testing and SIBO treatment protocols, head over to GHT Academy.

Schedule a free discovery call with our team here.